I have this same problem. A few things I have noticed:
1. If I connect to a bluetooth dialer, I do not have the problem. So, I could be trying to make a call from the phone and fail, walk out and pair it with my truck, then dial from the truck's touch screen, and it will dial just fine.
2. Going in and out of airplane mode often cures the problem. (Not sure if it is always or sometimes - need to try it a few more times.)
3. It seems related to the other problem that crept up at a similar time - the keyboard will show up and show me typing, but no words will actually make it into the text entry box. Happens, with Swiftkey, Swype, and the HTC built-in kybd.