I copied the demo code directly from the Accordion section of http://angular-ui.github.com/bootstrap/ and it all works except that heading="{{group.title}}" does not resolve the title property. On my web page I get the accordion body text correctly but {{group.title}} is displayed as the title. What am I doing wrong?
As noted in the comment above it is impossible to diagnose the problem you are facing without seeing live code example. On the plunker forked from the demo page it works OK: plnkr.co/edit/OuDZna?p=preview
The only thing that comes to my mind that could cause such problematic behavior is the AngularJS version used. As noted in "Getting started" on http://angular-ui.github.com/bootstrap/ you need at least 1.0.4 (or 1.1.2 if you are on the unstable branch). There were some bugs in earlier versions of AngularJS that were breaking interpolation.