I think I am having this problem but just to make sure, can someone please describe it to me?
My dear friend This is to turn off the screen when you on a call so you don't press anything While you talking on the phone if you have updated to 4.1 You won't experience this problem
Au contraire, My dear friend. I have 4.1 and just today, three or four times in the same phone call I detected the screen lighting up. The phone was trying to call my doctor. Some message was on the screen saying something like "Press to return to your phone call."
Sounds like a proximity problem to me.