This could be some sort of CEC issue. What is a typical time interval between these random events? You could try connecting only one box to the TV. (Multiple boxes connected to a receiver that is then connected to the TV is not "one box" for the purpose of this experiment). I'd be looking for a box that announced to CEC that it was shutting down and the TV responded to this inappropriately.

There is a "feature" associated with some of the FIOS cable boxes that makes me nervous. After an interval of inactivity, they'll shut down. I haven't observed this causing any trouble for my installs, but I can't rule out that this shutdown could create some sort of CEC event. So far it has only been an annoyance that requires an extra Menu button press to "wake" the cable box -- that had to be already awake in order to recognize an IR command and issue the message.