Yes, I'm aware that. That's why I tried to think of scenarios where I was possibly using my other browsers/devices with the same gmail account. But, this is different. I just saw the same thing happening again with another gdocs document. The message comes up "hxxxxx has opened the document" and then some seconds later, "hxxxxx has left", while I wasn't doing anything. (If it wasn't due to some kind of anomoly in google docs, e.g., possibly as suggested spaghetti, then the only explanation seems somebody cracked my password, unfortunately.)