I haven't tried a memory test yet (will do now and get back to you), but I don't think this is the problem since Hugo has said before that they haven't had a single Mk2a with bad memory chips. (of course, with my luck...)
As said before, it's not like it's happening every half hour, so I can live with it. Who knows, maybe it will be solved with a new firmware. (I'm actually awaiting the newest beta. Didn't try one yet because I wanted the biggest bugs ironed out first - I guess that must have happenend by now, so...)