Bootstrap3 bis2 Accordion & Collapse

I've build the Bootstrap3_bis2 solution, but I see that in the Demo Accordion and Collapse don't work properly, as they remain always collapsed.
I've seen that the problem is in the Collapse module, because the expand method never switches the class ".collapse" (which has display:none) with the class ".in".

.collapse {
  display: none;
}

.collapse.in {
  display: block;
}


I see that Bootstrap 3 Js also sets a "collapsing" class during collapse/expand (maybe useless with angular-ui javascript):

.collapsing {
  position: relative;
  height: 0;
  overflow: hidden;
  -webkit-transition: height 0.35s ease;
          transition: height 0.35s ease;
}

Thank you,
Matteo