Thanks, zulzedd. I had forgotten about your earlier post - back then I had not yet tried pool mining so it went right over my head at the time.

Sounds like we have similar effects when pool mining. Did you notice whether the address your pool mining payouts went to was normal (presumably your default/leaderboard address)? Mine - only the one so far - showed as being sent to a receiving address I use for a different purpose, one that the mining pool presumably should not have been aware of. I'm now guessing it's a glitch in the wallet display - perhaps it shows "last referenced address" or some such thing.

I'll keep this machine in pool mode a while longer and see what develops.