I am experiencing this regularely on my two players. I believe to have nailed it down to Hijack beeing the source for this. The players run fine with a standard image, but as soon as Hihack is installed I get random jumps to standby mode. In DC Mode as well as in AC mode. No Timer was activated in Hijack. I even set the timer action to beep to see if it would now start to beep in random intervals, but it still kept going to standby. So it doesn't seem to be directely timer related, but must still be something within the hijack code.
I don't think the cause are foreign IR sources. The very same empeg at the very same place, runs fine with a standard beta image but drops to standby here and then with a Hijack kernel.