Display freezing on call

[mauer8]

I have a HTC Thunderbolt.  It has happened to me about 4 times so far, where I will be on a call and my phone display will freeze.  Or I will be on a call and the mute button will accidentally be hit and then freeze.  I would like to know how to fix this.  It is really annoying.  I have to just wait until the person hangs up and then it goes back to normal. 

It may also have to due with the sensor on the front of my phone doesn't seem to work correctly all the time.  Almost every time I just have to hit the phone lock button to lock the screen.

Please Help!!

[AZSALUKI]

Do you have long enough hair to be getting in between your ear and the sensor? I've seen people resolve similar issues by making sure all of their hair is pulled back behind their ear.