In which way is it not working?
If you are trying to minimise an incoming call , which you have not answered yet (if this is the actual scenario) - it wont work and we have threads discussing this already on ZenTalk. It's not a bug per-se but a polarizing functionality.
If you are already in a call, talking, and want to minimize the call screen - you use your regular methods to return back to home. (Back button, swap apps, press home/gesture to home, etc).
