I recently changed from DISH to Comcast because because they offered more HDTV programming in this area. In six weeks, I've had the Motorola DCT6412 replaced three times (most recently yesterday morning).
With each DVR, after some time interval, the unit eventually 'resets' itself while trying to select a program to record from the on-screen guide. At some point while scrolling through the guide when I push the 'Select' button, the DVR display goes blank, there is a loud click, then has a '-' (hyphen) and the channel number finally reappears. Each time, however, it dumps the entire guide and has to start re-downloading again (which has been taking in excess of 24 hours). The last time, all the recorded material (HD movies) was deleted as well as the listings for all scheduled recordings.
The Comcast service people said they'd never seen anything like it and I can find no mention of such a problem in any of the forums here. They've tested the line and connections :( several times and find no faults there. I'm using the original remote that came with the first box. Is it possible the remote control could be sending some rogue command that tells the DVR to reset? I had a DVR with DISH for a couple years and never experienced anything even remotely similar.