Add class to accordion heading using angualr ui bootstrap?

Add class to accordion heading using angualr ui bootstrap?

I want use ng-class to conditionally add a class to the accordion-heading,
but it appears that not even setting a class explicitly on the element
gets preserved. I have this:
<div accordion close-others="true">
<div ng-repeat="currItem in items" accordion-group>
<div accordion-heading class="myClass">My Heading {{$index}}</div>
<div class="accordion-inner myClass">asdf asdf asdf</div>
</div>
</div>
And the fiddle: http://jsfiddle.net/Zmhx5/1/
When I inspect the accordion heading element, the class myClass is nowhere
to be found. Is there some reason I can't add classes to the accordion
heading?