I had/have this same problem. At first I thought my display had died... but a power cycle "fixed" it.

I immediately mailed empeg, and Hugo explained it was a known bug. I'm not sure if it's acceptable
to repost his mail to me, but the gist of it was that he knows it has something to do with the display
PIC losing track of where the start of the fame is. He also said that he's only seen the problem three
times himself (and gave me the impression he hadn't gotten any other reports at that time) so hadn't
been able to reliably reproduce it for debugging.

That response was enough for me, just to know that it wasn't an indicator of premature display failure.
I was very worried it was a hardware problem and was happy to hear it was just a software bug.
I don't expect to have it fixed, since this kind of problem isn't necessarily field upgradable (removing
the PIC from the display board and reprogramming it) for most people.

I saw the problem 6 weeks ago, and haven't seen it since, despite using the empeg for many hours a
day, every day. If the problem does show up again, I know a reboot will fix it. IMHO, this puts it in the
class of "minor annoyance".

Let me publicly thank Hugo and the empeg crew for their honesty about disclosing the existence of
such problems, and the promptness of their responses to customers.

-j