Mine only does it when it has been turned off, it gets confused in start up and switches back and forth from landscape/portrait until I do, as you said, deactivate then lock again. Never did this in 5 or 5.1, so I think it is OS software issue ... It's not a great drama, just wondered if it was happening anywhere else. Have also had a few app crashes, and have 2 apps, a fotopedia and guardian photo app that have got stuck halfway in updating. I was going to hold off on updating iPad, but I will soon order iPhone and want to get these and my MacBook Air playing nicely together. Still have snow leopard on my iMac, so if it all gets too glitchy I can turn them all off and get some work rather than tech troubleshooting done on my snowy mac which is, has always been, so stable, doesn't know this word glitch.
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Would appreciate if you would post here when you get your hardware checked. Thanks.