Not as suprising as one might think
I have myself wondered how common this is. More than once, I have woken up to find my laptop open, and a bunch of code modified that I have no memory of working on. Now, I can't say that I was sleep-programming, as it could be any number of things that cause you to not remember what you do late at night. For all I know, I could have woken up, coded in an effort to get back to sleep, and not remembered any of it. Who knows? (Sadly, my coworkers comment that my best code is the code I don't remember writing.)
Thing of it is, I never really considered it all that abnormal. I have a friend who is a painter, and she has been known to paint in her sleep. I know of at least two chronic sleepwalkers. I think that there needs to be a study on if this sort of thing really is "performing a complex activity while asleep" or simply "not remembering doing something." I.E. are you at that point experiencing REM sleep or not?
I always sort of thought of it like yarding out a flash drive from the system before the write buffer had finished emptying. The last bit of your day's memories just didn't get written. What are your guys' thoughts?