Mine happens mostly is web pages and doesn't seem to have anything to do with sleep mode or battery. It just seems to happen most of the time. I type something and then look back and the firts one or two letters I typed don't appear. I would never have bought this if I had know about this from the start. For $3000 I should expect a working kepboard.
As a recent Windows to Apple convert, I must say I never expected these sort of nagging issues with a Mac. First the Time Machine problems and now this. Yes I have the same darn keyboard problem on my brand new 17" MBP. This is ugly.