Mat-select disabled reactivity bug

[als9xd]

Reproduction

https://stackblitz.com/edit/angular-3wepre

Steps to reproduce:

1. Click "Select form 0"
2. Click "Delete form 0"
3. Click "Select form 1"

Expected Behavior

The "Object Type" field should not be disabled.

Actual Behavior

The UI for the "Object Type" field on form 1 is disabled even though the form's disabled property says otherwise. The weird thing is that the "First Name" field is not disabled which leads me to believe it is a bug with the mat-select specifically.

Environment

• Angular: 5.2.4
• CDK/Material :5.2.4
• Browser(s): Chrome
• Operating System (e.g. Windows, macOS, Ubuntu): Windows