Yes, I did indeed. I tried waiting half an hour the first time, and varying times up to 2 or 3 hours. No matter how long I let it warm up, either calibration routine brings it back to zero momentarily, then it starts to float up and down again all over the place within less than a minute. I don't mean a slow drift either. More like an oscillation. This happens whether I have no probe connected, have a probe connected and grounded, and even when displaying a signal.
This is running on battery also, and no stray signals around - again this doesn't happen on my bench scope when they're sitting within a couple feet of each other.