I have the same problem. However, WM6 (leaked) didn't solve this problem. And yes, IT IS ANNOYING!!
I just installed the unbranded WM6 ROM (for a locked ATT 750) and have disabled the touchscreen function during calls, and so far I haven't noticed this problem yet.
If anyone has talked to tech support or has come up with a fix/reason why this happens I would like to hear what they had to say.
Thanks.
