Avoiding "my cheek hung up on you" on an Optimus T? I upgraded my wife to an LG Optimus T from a G1, and she keeps accidentally hanging up on people with her cheek. She never had this problem with the G1.

I've asked her if she's locking the screen (by hitting the power button once) and she appears to be doing that but for some reason when she's on a call the screen appears to take input. 

At first I thought this was a problem with her face (heh), so I had her try it on my Nexus One and she can call, hit the power button to turn the screen off and then talk normally. 

Has anyone seen this kind of behavior before, and if it's just an annoyance is there maybe an application that can mitigate this?
It turns out that by avoiding touching it with her cheek she was turning the phone a bit and moving the proximity/light sensor away from her ear, which turned the screen on and was causing the hangups.

When she presses the speaker firmly against her ear the screen locks like it's supposed to.