Actual Behavior:

• What is the issue? *
  • mdSelect with "required" set in a form; use as empty option to clear select
  • select a non-empty option, form become valid
  • select empty option, form remains valid
• What is the expected behavior?
  • form should become invalid

CodePen (or steps to reproduce the issue): *

• CodePen Demo which shows your issue: http://codepen.io/dephiros/pen/ObMqBY?editors=1000
• Details:

Angular Versions: *

• Angular Version: 1.5.5
• Angular Material Version: 1.1.1

Additional Information:

• Browser Type: * chrome
• Browser Version: * latest
• OS: * macOS
• Stack Traces: