HTC Droid Eris : Calls Straight To Voice Mail

One day about 3 weeks ago I missed a few calls from a friend because the phone did not ring.I had a special ringtone assigned to the person, so I checked to see if there was something wrong with the person's Contacts entry that would make the phone not ring.When I looked, the box was checked where it says "Send calls directly to voicemail".I know that I never checked that box intentionally, so I unchecked it.That was about 3 weeks ago.Yesterday the same person called 3 times and the phone never rang, so I looked at the Contacts entry again and, sure enough, the box was checked again!I carry my phone in a holster on my belt, so it can't be that the box was inadvertently checked by the phone moving around in my pocket.Has anyone else had this experience?