I have a new iMac 27" and my wife has an iPad. I checked on the iPad and the only thing I could think of was something to do with the
lock unlock which turns the screen of and on with the cover.
You can also check in settings/
(or whichever you use)
You probably tried these, but my favourite place to ask questions like this is http://www.mac-forums.com/
and look about half way down at the iPad section. I find that there is a lot of very helpful folks there.