...a sign that your newly-purchased open box Denon DVM-2815 DVD player really is broken, that your cheap-ass cables don't work so well, or that there's something wrong with that input selector on the TV, which had only previously seen 480i signals. The problem occurred this morning. I switched the HDTV-cable and DVD input cables on the TV, and haven't seen the problem since. Any ideas on what to change/what to do to diagnose the problem? If it's the DVD player, obviously I need to send it back pretty soon.

...so short of this taking a month or two to confirm, I was hoping of another way.