My ringer problem *seems* to be fixed by ditching the HTC finger-friendly volume control app and switching back to using the default system volume control.
http://www.jcerna.com/highlife22/NoVolume.cab
I went through the motions of trying to kill the ringer (volume up/down, vibrate on/off, silent/audible, etc) and while it's only been a few minutes, my ringer hasn't shut off yet. YMMV. I'll probably have to check back in a couple days to see if it's fixed.