I would have suspected the usual suspects, except that it happened to me with my Harmony 900 too. My parents had the same issue last week with their DirecTv remote at their house. Ill chalk it up to a software bug I guess, and instruct mom how to hit the select button or exit if it does it again.
Interesting, Dave. I just had an HR44 installed which does a weird thing. Installer put in new stuff on the dish and new splitter since I didn't have a SWM before. Also connected is older HR22 and H21.
During the first hour or so when first turned on in the morning, the HR44 will just tune up one channel all by itself. Seems to do it 2-4 times in the first hour, then maybe again once a couple hours later. What is interesting is that it doesn't display a banner when the channel changes like it would if you do it with a remote. I've considered all the possible IR sources and buried the remotes so they don't point toward the tv or any reflective surface. Still does a channel change. Also disconnected the other receivers in case they were feeding signals back.
Wondered if it was the router doing something weird. I'm going to disconnect the internet cable to see if it does the same thing just to eliminate the possibility there is something strange coming down that line into the HR44.
Tech support at Directv didn't have a solution but said they could send out a tech. Don't know what they would do except replace all the new stuff they just installed. Doesn't seem to be widespread, but having similar problems in Central AR is not normal, Looks like a software issue since you have a different model unit than I do. Or the NSA could be spying on us :^)