Screen issues while talking on the phone?

[dirty socks]

I just picked up the Lumia 920 during black friday. I've noticed that when i'm on the phone and also playing games (words with friends) that the screen then gets unresponsive. Like say if I were to choose the letter C and place it to the spot I like on the game. It won't let me! Sometimes I can't even select the letters at all. Is anyone else having this issue?!