[op12]

I have a Sprint TP2 and was having the same issue, which was most annoying when in a call and trying to get access to the keypad or "End Call" button...once the proximity sensor had shut off the screen, I could get the screen to come back, but the keypad/phone screen would only appear for a second and then disappear and I was back at the home screen while the call continued.

I had the device lock enabled so I tried changing the setting to 0 minutes as suggested. This made the screen work correctly with applications, but the in-call screen was still disappearing. Turning off the device lock completely solved the problem. I wanted to mention this since I haven't installed anything other than Google Maps, so it seems to be solely a TF3D issue.