Issue 1:
When the yaml parser reads

foo: bar
foo: bar2

It will return an array with the first key. This is unfortunate for a couple of reasons.

It is not to spec. The Yaml spec is clear that duplicate keys should be treated as an error - see http://yaml.org/spec/1.2/spec.html#id2759572

The current behaviour of choosing the first key is pretty unique. See:

Psy Shell v0.7.0 (PHP 7.0.7 — cli) by Justin Hileman
>>> $a = ['a' => '1', 'a' => '2']
=> [
"a" => "2",
]

Also it is the opposite behaviour to the PECL yaml parser (which behaves like PHP) so allowing users to swap between implementations can have interesting affects.

Issue 2:
Q
A

Bug report?
yes

Feature request?
no

BC Break report?
/no

RFC?
no

Symfony version
3.4.5

The toolbar seems to break page ajax requests when it is shown. Ajax request are made with jQuery.get() function as regular usage.

I've tryed hiding the toolbar with following configuration :

#app/config/config_dev.yml
web_profiler:
toolbar: false

All ajax requests works fine.

Also, by setting the excluded_ajax_paths to '.*, it allows all requests to finish correctly.

#app/config/config_dev.yml
web_profiler:
toolbar: true
excluded_ajax_paths: '.*'

It also affects a SF4 basic project without any vendors other than symfony bundles and components.

Here the composer info :

behat/gherkin v4.5.1 Gherkin DSL parser for PHP 5.3
behat/transliterator v1.2.0 String transliterator
bentools/cartesian-product 1.2 A simple, low-memory footprint function to generate all combinations from a multi-dimensionnal array.
clue/stream-filter v1.4.0 A simple and modern approach to stream filtering in PHP
cocur/slugify v3.1 Converts a string into a slug.
codeception/codeception 2.4.0 BDD-style testing framework
codeception/phpunit-wrapper 6.0.5 PHPUnit classes used by Codeception
codeception/stub 1.0.2 Flexible Stub wrapper for PHPUnit's Mock Builder
composer/ca-bundle 1.1.0 Lets you find a path to the system CA bundle, and includes a fallback to the Mozilla CA bundle.
data-uri/data-uri 0.2.5 PHP DataURI component
data-uri/twig-extension 1.0.1 Twig extension for data URI ; Converts data to the data URI Url scheme (RFC 2397)
doctrine/annotations v1.6.0 Docblock Annotations Parser
doctrine/cache v1.7.1 Caching library offering an object-oriented API for many cache backends
doctrine/collections v1.5.0 Collections Abstraction library
doctrine/common v2.8.1 Common Library for Doctrine projects
doctrine/data-fixtures v1.3.0 Data Fixtures for all Doctrine Object Managers
doctrine/dbal v2.6.3 Database Abstraction Layer
doctrine/doctrine-bundle 1.8.1 Symfony DoctrineBundle
doctrine/doctrine-cache-bundle 1.3.2 Symfony Bundle for Doctrine Cache
doctrine/doctrine-fixtures-bundle v2.4.1 Symfony DoctrineFixturesBundle
doctrine/doctrine-migrations-bundle v1.3.1 Symfony DoctrineMigrationsBundle
doctrine/inflector v1.3.0 Common String Manipulations with regard to casing and singular/plural rules.
doctrine/instantiator 1.1.0 A small, lightweight utility to instantiate objects in PHP without invoking their constructors
doctrine/lexer v1.0.1 Base library for a lexer that can be used in Top-Down, Recursive Descent Parsers.
doctrine/migrations v1.6.2 Database Schema migrations using Doctrine DBAL
doctrine/orm v2.5.14 Object-Relational-Mapper for PHP
egulias/email-validator 2.1.3 A library for validating emails against several RFCs
elasticsearch/elasticsearch v6.0.1 PHP Client for Elasticsearch
facebook/webdriver 1.5.0 A PHP client for Selenium WebDriver
fig/link-util 1.0.0 Common utility implementations for HTTP links
friendsofsymfony/elastica-bundle v5.0.3 Elasticsearch PHP integration for your Symfony project using Elastica
friendsofsymfony/jsrouting-bundle 1.6.3 A pretty nice way to expose your Symfony2 routing to client applications.
friendsofsymfony/oauth-server-bundle 1.5.2 Symfony2 OAuth Server Bundle
friendsofsymfony/oauth2-php 1.2.3 OAuth2 library
friendsofsymfony/rest-bundle 2.3.1 This Bundle provides various tools to rapidly develop RESTful API's with Symfony
fzaninotto/faker v1.7.1 Faker is a PHP library that generates fake data for you.
gedmo/doctrine-extensions v2.4.33 Doctrine2 behavioral extensions
guzzlehttp/guzzle 6.3.0 Guzzle is a PHP HTTP client library
guzzlehttp/promises v1.3.1 Guzzle promises library
guzzlehttp/psr7 1.4.2 PSR-7 message implementation that also provides common utility methods
guzzlehttp/ringphp 1.1.0 Provides a simple API and specification that abstracts away the details of HTTP into a single PHP function.
guzzlehttp/streams 3.0.0 Provides a simple abstraction over streams of data
h4cc/wkhtmltoimage-amd64 0.12.4 Convert html to image using webkit (qtwebkit). Static linked linux binary for amd64 systems.
h4cc/wkhtmltopdf-amd64 0.12.4 Convert html to pdf using webkit (qtwebkit). Static linked linux binary for amd64 systems.
hamcrest/hamcrest-php v2.0.0 This is the PHP port of Hamcrest Matchers
html2text/html2text 4.1.0 Converts HTML to formatted plain text
imagine/imagine v0.7.1 Image processing for PHP 5.3
incenteev/composer-parameter-handler v2.1.3 Composer script handling your ignored parameter file
jdorn/sql-formatter v1.2.17 a PHP SQL highlighting library
jeroendesloovere/vcard 1.5.2 This VCard PHP class can generate a vCard with some data. When using an iOS device it will export as a .ics file because iOS devices don't support the default .vcf files.
jeroendesloovere/vcard-bundle 1.2.2 This Symfony 2 bundle can generate vCards with lots of data. When using an < iOS 7 device it will export as a .ics file because iOS devices don't support the default .vcf files.
jms/metadata 1.6.0 Class/method/property metadata management in PHP
jms/parser-lib 1.0.0 A library for easily creating recursive-descent parsers.
jms/serializer 1.11.0 Library for (de-)serializing data of any complexity; supports XML, JSON, and YAML.
jms/serializer-bundle 2.3.1 Allows you to easily serialize, and deserialize data of any complexity
knplabs/gaufrette v0.5.0 PHP library that provides a filesystem abstraction layer
knplabs/knp-components 1.3.5 Knplabs component library
knplabs/knp-gaufrette-bundle v0.5.2 Allows to easily use the Gaufrette library in a Symfony project
knplabs/knp-menu 2.3.0 An object oriented menu library
knplabs/knp-menu-bundle v2.2.1 This bundle provides an integration of the KnpMenu library
knplabs/knp-paginator-bundle v2.7.2 Paginator bundle for Symfony to automate pagination and simplify sorting and other features
knplabs/knp-snappy v1.0.4 PHP5 library allowing thumbnail, snapshot or PDF generation from a url or a html page. Wrapper for wkhtmltopdf/wkhtmltoimage.
knplabs/knp-snappy-bundle v1.5.2 Easily create PDF and images in Symfony2 by converting Twig/HTML templates.
kriswallsmith/assetic v1.4.0 Asset Management for PHP
leafo/scssphp v0.7.5 scssphp is a compiler for SCSS written in PHP.
league/uri 5.2.0 URI manipulation library
league/uri-components 1.7.1 URI components manipulation library
league/uri-hostname-parser 1.1.1 ICANN base hostname parsing implemented in PHP.
league/uri-interfaces 1.0.0 Common interface for URI representation
league/uri-manipulations 1.4.0 URI manipulation library
league/uri-parser 1.3.0 userland URI parser RFC 3986 compliant
league/uri-schemes 1.1.1 URI manipulation library
lexik/maintenance-bundle v2.1.5 This bundle allows you to place your website in maintenance mode by calling two commands from your console.
liip/imagine-bundle 1.9.1 This bundle provides an image manipulation abstraction toolkit for Symfony-based projects.
michelf/php-markdown 1.8.0 PHP Markdown
mikey179/vfsStream v1.6.5 Virtual file system to mock the real file system in unit tests.
mockery/mockery 1.0 Mockery is a simple yet flexible PHP mock object framework for use in unit testing with PHPUnit, PHPSpec or any other testing framework. Its core goal is to offer a test double framework with a succinct API capable of clearly defining all possible object ope...
monolog/monolog 1.23.0 Sends your logs to files, sockets, inboxes, databases and various web services
myclabs/deep-copy 1.7.0 Create deep copies (clones) of your objects
nelmio/alice v2.3.4 Expressive fixtures generator
nelmio/api-doc-bundle 2.13.3 Generates documentation for your REST API from annotations
ocramius/package-versions 1.3.0 Composer plugin that provides efficient querying for installed package versions (no runtime IO)
ocramius/proxy-manager 2.1.1 A library providing utilities to generate, instantiate and generally operate with Object Proxies
oro/doctrine-extensions 1.2.0 Doctrine Extensions for MySQL and PostgreSQL.
pagerfanta/pagerfanta v1.0.5 Pagination for PHP 5.3
paragonie/random_compat v2.0.11 PHP 5.x polyfill for random_bytes() and random_int() from PHP 7
payum/iso4217 1.0.1 ISO 4217 PHP Library
payum/payum 1.5.0 One million downloads of Payum already! Payum offers everything you need to work with payments. Friendly for all PHP frameworks (Symfony, Laravel, Zend, Yii, Silex). Check more visiting site.
payum/payum-bundle 2.3.0 One million downloads of Payum already! Payum offers everything you need to work with payments. Check more visiting site.
phar-io/manifest 1.0.1 Component for reading phar.io manifest information from a PHP Archive (PHAR)
phar-io/version 1.0.1 Library for handling version information and constraints
php-http/guzzle6-adapter v1.1.1 Guzzle 6 HTTP Adapter
php-http/httplug v1.1.0 HTTPlug, the HTTP client abstraction for PHP
php-http/message 1.6.0 HTTP Message related tools
php-http/message-factory v1.0.2 Factory interfaces for PSR-7 HTTP Message
php-http/promise v1.0.0 Promise used for asynchronous HTTP requests
phpcollection/phpcollection 0.5.0 General-Purpose Collection Library for PHP
phpdocumentor/reflection-common 1.0.1 Common reflection classes used by phpdocumentor to reflect the code structure
phpdocumentor/reflection-docblock 4.3.0 With this component, a library can provide support for annotations via DocBlocks or otherwise retrieve information that is embedded in a DocBlock.
phpdocumentor/type-resolver 0.4.0
phpoption/phpoption 1.5.0 Option Type for PHP
phpspec/prophecy 1.7.5 Highly opinionated mocking framework for PHP 5.3+
phpunit/php-code-coverage 5.3.0 Library that provides collection, processing, and rendering functionality for PHP code coverage information.
phpunit/php-file-iterator 1.4.5 FilterIterator implementation that filters files based on a list of suffixes.
phpunit/php-text-template 1.2.1 Simple template engine.
phpunit/php-timer 1.0.9 Utility class for timing
phpunit/php-token-stream 2.0.2 Wrapper around PHP's tokenizer extension.
phpunit/phpunit 6.5.7 The PHP Unit Testing framework.
phpunit/phpunit-mock-objects 5.0.6 Mock Object library for PHPUnit
polishsymfonycommunity/symfony-mocker-container v1.0.2 Provides base Symfony dependency injection container enabling service mocking.
psr/cache 1.0.1 Common interface for caching libraries
psr/container 1.0.0 Common Container Interface (PHP FIG PSR-11)
psr/http-message 1.0.1 Common interface for HTTP messages
psr/link 1.0.0 Common interfaces for HTTP links
psr/log 1.0.2 Common interface for logging libraries
psr/simple-cache 1.0.1 Common interfaces for simple caching
ramsey/uuid 3.7.3 Formerly rhumsaa/uuid. A PHP 5.4+ library for generating RFC 4122 version 1, 3, 4, and 5 universally unique identifiers (UUID).
react/promise v2.5.1 A lightweight implementation of CommonJS Promises/A for PHP
ruflin/elastica 6.0.1 Elasticsearch Client
sebastian/code-unit-reverse-lookup 1.0.1 Looks up which function or method a line of code belongs to
sebastian/comparator 2.1.3 Provides the functionality to compare PHP values for equality
sebastian/diff 2.0.1 Diff implementation
sebastian/environment 3.1.0 Provides functionality to handle HHVM/PHP environments
sebastian/exporter 3.1.0 Provides the functionality to export PHP variables for visualization
sebastian/global-state 2.0.0 Snapshotting of global state
sebastian/object-enumerator 3.0.3 Traverses array structures and object graphs to enumerate all referenced objects
sebastian/object-reflector 1.1.1 Allows reflection of object attributes, including inherited and non-public ones
sebastian/recursion-context 3.0.0 Provides functionality to recursively process PHP variables
sebastian/resource-operations 1.0.0 Provides a list of PHP built-in functions that operate on resources
sebastian/version 2.0.1 Library that helps with managing the version number of Git-hosted PHP projects
sensio/distribution-bundle v5.0.21 Base bundle for Symfony Distributions
sensio/framework-extra-bundle v3.0.29 This bundle provides a way to configure your controllers with annotations
sensio/generator-bundle v3.1.7 This bundle generates code for you
sensiolabs/security-checker v4.1.8 A security checker for your composer.lock
sonata-project/admin-bundle 3.32.0 The missing Symfony Admin Generator
sonata-project/block-bundle 3.12.0 Symfony SonataBlockBundle
sonata-project/cache 2.0.1 Cache library
sonata-project/core-bundle 3.9.1 Symfony SonataCoreBundle
sonata-project/datagrid-bundle 2.3.1 Symfony SonataDatagridBundle
sonata-project/doctrine-orm-admin-bundle 3.4.2 Symfony Sonata / Integrate Doctrine ORM into the SonataAdminBundle
sonata-project/exporter 1.8.0 Lightweight Exporter library
sonata-project/intl-bundle 2.4.0 Symfony SonataIntlBundle
sparkling/vat-bundle 0.2.0 A Symfony2 Bundle that checks a european VAT number
stfalcon/tinymce-bundle v2.2.0 This Bundle integrates TinyMCE WYSIWYG editor into a Symfony2 project.
stof/doctrine-extensions-bundle v1.3.0 Integration of the gedmo/doctrine-extensions with Symfony2
swiftmailer/swiftmailer v6.0.2 Swiftmailer, free feature-rich PHP mailer
sylius-labs/association-hydrator v1.1.0 Doctrine ORM hydration performance optimization made easier.
sylius/sylius v1.1.1 E-Commerce platform for PHP, based on Symfony framework.
symfony/assetic-bundle v2.8.2 Integrates Assetic into Symfony2
symfony/monolog-bundle v3.2.0 Symfony MonologBundle
symfony/phpunit-bridge v3.4.5 Symfony PHPUnit Bridge
symfony/polyfill-apcu v1.7.0 Symfony polyfill backporting apcu_* functions to lower PHP versions
symfony/polyfill-iconv v1.7.0 Symfony polyfill for the Iconv extension
symfony/polyfill-intl-icu v1.7.0 Symfony polyfill for intl's ICU-related data and classes
symfony/polyfill-mbstring v1.7.0 Symfony polyfill for the Mbstring extension
symfony/security-acl v3.0.1 Symfony Security Component - ACL (Access Control List)
symfony/swiftmailer-bundle v3.2.0 Symfony SwiftmailerBundle
symfony/symfony v3.4.5 The Symfony PHP framework
symfony/thanks v1.0.6 Give thanks (in the form of a GitHub ⭐) to your fellow PHP package maintainers (not limited to Symfony components)!
theseer/tokenizer 1.1.0 A small library for converting tokenized PHP source code into XML and potentially other formats
twig/extensions v1.5.1 Common additional features for Twig that do not directly belong in core
twig/twig v2.4.6 Twig, the flexible, fast, and secure template language for PHP
webmozart/assert 1.3.0 Assertions to validate method input/output with nice error messages.
white-october/pagerfanta-bundle v1.1.2 Bundle to use Pagerfanta with Symfony2
willdurand/hateoas 2.10.0 A PHP library to support implementing representations for HATEOAS REST web services
willdurand/hateoas-bundle 1.4.0 Integration of Hateoas into Symfony2.
willdurand/js-translation-bundle 2.6.6 A pretty nice way to expose your translation messages to your JavaScript.
willdurand/jsonp-callback-validator v1.1.0 JSONP callback validator.
willdurand/negotiation v2.3.1 Content Negotiation tools for PHP provided as a standalone library.
winzou/state-machine 0.3.3 A very lightweight yet powerful PHP state machine
winzou/state-machine-bundle v0.3.1 Bundle for the very lightweight yet powerful PHP state machine
zendframework/zend-code 3.3.0 provides facilities to generate arbitrary code using an object oriented interface
zendframework/zend-eventmanager 3.2.0 Trigger and listen to events within a PHP application
zendframework/zend-hydrator 2.3.1
zendframework/zend-stdlib 3.1.0