I see this on my iPad 3 all the time, and also on my big NEC. It's not really burn-in, but there is a VERY noticeable effect there. If I leave my iPad 3 in an app that has an easily-recognized pattern for a 10-15 minutes, then go to something with a smooth screen, I will see that "burn-in". It's totally normal, so far as I can tell; I got all excited when it happened to my NEC, then I started reading threads and found that basically all IPS displays have ... well, I want to call it phosphor memory, but obviously that's wrong.
Edit: And no, it's not a "polarizer defect". IPS displays do not work quite the same way other LCDs do, and this is normal for them.
so it's IR then.. image retention... which is temp not perm... I would hope Lloyd would know the difference.