Callbacks doesn't work for accordion

I'm trying to attach callbacks with accordion. As per the documentation it extends from the collapse component which seems to support callbacks such as expanding, collapsing etc.

So I tried adding the following:

<uib-accordion-group heading="first" collapsing="alert('collapsing')">
      first
</uib-accordion-group>

plnkr demo

Which I expect to work since accordion is an expansion of collapse. Is this a bug or am I doing something wrong..?

Version of Angular, UIBS, and Bootstrap

Angular: 1.5.3

UIBS: 1.3.1

Bootstrap: 3.3.6