Yes! So annoying! Seems like I have to reboot the box almost every day because of this.
Have you tried the "soft reboot" where you hold the power key for some length of time? I just read about that today, but haven't had a chance to try it yet. Is your 6412 is a place where ventilation could be a problem? Mine is in a cabinet with what seems like plenty of space, but still seems to get pretty hot.
Since you also have this jitter problem, I wonder if you also experience my other major annoyance with this box - the delayed response to the remote commands? Seems like the box just stops responding for some amount of time (can be as long as >1 minute). And, naturally, I'm hitting a button now and again to see if the box has woken up, only to find that it buffered all my remote commands, and "plays them all back" which has actually resulted in a deleted recording a few times!!
Well, aside from the deleted recordings, just wondering if you've experienced both problems together, or if you only see the jitter...?