Segmentation Fault with optional callable

When using an optional param that is supposed to be callable, I'm getting "Segmentation fault: 11"

Again, I don't know any C, but the test case in this pull request does reproduce always on my machine. I'm using Mac OS X Mavericks with homebrew php. Here's the summary wall from `make test`:

=====================================================================
PHP         : /usr/local/Cellar/php55/5.5.8/bin/php 
PHP_SAPI    : cli
PHP_VERSION : 5.5.8
ZEND_VERSION: 2.5.0
PHP_OS      : Darwin - Darwin CAP-MBP-45.local 13.0.0 Darwin Kernel Version 13.0.0: Thu Sep 19 22:22:27 PDT 2013; root:xnu-2422.1.72~6/RELEASE_X86_64 x86_64
INI actual  : /Volumes/Sources/vendors/augmented_types-git/tmp-php.ini
More .INIs  :  
CWD         : /Volumes/Sources/vendors/augmented_types-git
Extra dirs  : 
VALGRIND    : Not used
=====================================================================

Let me know if there's any more info I can give you to help with this.