[oooanickel]

Was having the same issue and found this thread. Opened my keyboard shortcut prefs to see if there was something weird going on. (Since accidental update to Mavericks, and I didn't really feel like blowing out all of my custom commands.) An additional menu option popped up for shortcuts - Inputs. command + space seems to have been selected as an option for cycling inputs in this weird menu I've never seen before. I unchecked that box, closed out of prefs and everything's fine now. I was going to reopen the pref window to post an image here, but miraculously that menu has disappeared. Very fishy.