Keep phone from muting when dialing numbers in a call

[mslaney]

When I use the keypad to send DTMF tones I believe that my phone is muting as I often have trouble with people being able to hear me after a menu selection. This isn't completely reproducible that I can tell, but it happens enough that it's a problem. I'm using an HTC Imagio (Whitestone). I think it's an issue with WM, the touchscreen, and light sensor that tells the phone it's against my face, but it may be device specific. Any insight? A registry key to disable this automatic mute "feature" when dialing numbers in a call?