Repository: angular
Issue: Reactive Form is disabled but disabled property is false
Labels: type: bug/fix,freq2: medium,area: forms,state: confirmed,forms: disabling controls,P3

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# 🐞 bug report

### Affected Package
<!-- Can you pin-point one or more @angular/* packages as the source of the bug? -->
<!-- ✍️edit: --> The issue is caused by package @angular/forms


### Description
I have simple reactive form with some input fields.
The method `form.disable()` is called to disable the form and all fields.
The method works, as all input fields in the UI are now disabled.

**Expected**  
The property `form.disabled` should be `true` as the form is disabled now.

**Actual**  
The property `form.disabled` is `false`.

**Cause of the problem**  
After building the form, I subscribe to control `f1` and update the value of another control whenever `f1` changes. 

```
this.myForm.controls.f1
  .valueChanges
  .subscribe(() => this.testMethod());

testMethod() {
  this.myForm.controls.f3.setValue('test');
}
```

**Workaround**  
It works when I call `form.disable()` twice.


## 🔬 Minimal Reproduction
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https://stackblitz.com/edit/angular-issue-repro2-g8725l



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## 🌍  Your Environment

**Angular Version:**
<pre><code>
<!-- run `ng version` and paste output below -->
<!-- ✍️-->
Angular CLI: 7.3.5
Node: 10.14.1
OS: win32 x64
Angular: 7.2.9
... animations, common, compiler, compiler-cli, core, forms
... http, language-service, platform-browser
... platform-browser-dynamic, router

Package                            Version
------------------------------------------------------------
@angular-devkit/architect          0.13.5
@angular-devkit/build-angular      0.13.5
@angular-devkit/build-optimizer    0.13.5
@angular-devkit/build-webpack      0.13.5
@angular-devkit/core               7.3.5
@angular-devkit/schematics         7.3.5
@angular/cdk                       7.3.4
@angular/cli                       7.3.5
@angular/material                  7.3.4
@angular/material-moment-adapter   7.3.4
@ngtools/webpack                   1.10.2
@schematics/angular                7.3.5
@schematics/update                 0.13.5
rxjs                               6.4.0
typescript                         3.2.4
webpack                            4.29.6
</code></pre>

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