Did you get a screen grab?

I did - and it looked fine in the screen grab both times.

I got a call back from the Genius this afternoon, and he basically confirmed what I had guessed - it is limited to the App Store, and is at this time not something they think can be fixed by replacing hardware. He said it happened on his phone as well a few times, and that anything that redraws the screen will fix it. So that's why when I took the screen grab, the white flash happened and forced a refresh, which fixed the corrupted pixels. Next time it happens, I'm going to try hiding and restoring the keyboard to test that.

Interestingly, when I talked to him about the purple glare around bright lights, he said it was the first anyone had talked to him about it. I said "Ok, I guess *that*'s the party line on the purple glare, then..."

So, right now - wait and see. It's currently looking like a software issue in the App Store app, which is cosmetic only, so I'm not going to take any time out of my day to try and fix it. I'll keep you posted if I get any info that confirms or contradicts that theory.