(md-menu) cursor is trapped if md-menu is destroyed too early

[clshortfuse]

Actual behavior:
If md-menu is destroyed too quickly after a menu is fired, the cursor focus is lost completely.

CodePen or Steps to reproduce the issue: *
http://codepen.io/shortfuse/pen/XKXPvJ
At about 300-400 timeout the cursor gets trapped

Angular Versions: *
master

Additional Information:
Chrome v50/v51

[clshortfuse]

It might be this line: https://github.com/angular/material/blob/master/src/components/menu/js/menuController.js#L174

   return self.isOpen ? $mdMenu.destroy() : $q.when(false);

It seems as though If the menu doesn't get a chance to fully open, it isn't properly destroyed.

It might also be possible to fix this by making sure md-backdrop is a child of md-menu instead of body. That way md-backdrop's destruction is automatic. I'm not sure what repercussions there may be though.