Collapse inside collapse not working as expected with example

[W1zzard]

If i use collapse inside other collapse inner collapse not working as expected:
http://plnkr.co/edit/DTY72Zf7dX3QqN6jwtcj?p=preview
toggle collapse, then toggle inner collapse, then close outer and close inner, open outer, inner still open but should be closed.

[chrisirhc]

Should be fixed via #1444

[chrisirhc]

Possibly duplicate of #1774