is-open attribute not working correctly when accordion is hidden

[ebelanger]

http://plnkr.co/edit/iWHWYJ

There seems to be a resizing bug when the accordion is hidden. Tried hiding with ng-show in this exemple, but hiding with ng-class="{hide: !show}" did the same thing.

Seems to only happen if the accordion is hidden on initial load. Once you close and re-open the bugged group, it is possible to hide and show the accordion without any problems.

[petebacondarwin]

I think this is the same problem as in #82