I get this message all the time. Even when the Iphone has been put into sleep mode, it still comes back with "nothing to undo" and the option to cancel. Everybody is having this problem. Apple *** ? are you monitoring these discussions.
I found this thread after searching for "nothing to undo." Yes, the acceleometer is all very innovative and pioneering, blah blah. We get it. This shake to undo, though, takes it to an obnoxious and childish level. A disable button for this must be the first thing they add for 3.01.