Pode - thanks. I'm not sure that's it though as the demo bug page they show works fine on my io6 iPad 3. I also tried adding both pieces of code to the page and neither of them seemed to fix it. I might have done it wrong though, as I don't know how to write HTML or JavaScript well.
Edit: I should mention this post in another thread where I found the exact pixel height at which the bug occurs, if that might help any: http://www.scirra.com/forum/forum_posts.asp?TID=58532&PID=360878&title=my-game-lags-in-landscape#360878
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Kind of strange. On my ipad 2 (no retina mode, obviously), it keeps around 460 or so objects in either landscape or vertical at about 60fps. It makes no difference, though it does crop the text off some in vertical.