When I am typing articles (I write for a newspaper), I am continually hitting some mystery key that suddenly brings up a random older story file that I suddenly find myself typing on. This is maddening and really breaks up my concentration to have to close that file, unsaved, and return to the new file.

What am I doing that's causing this? Is there any setting or other thing I can do to stop it from happening? I can't imagine why this is a feature, because I can see nothing useful in it -- especially since it seems to bring up totally random older files.