Files disappearing but not closing??

Hello!  My coworkers and I have been having an issue where we close an Illustrator file but it isn't actually closing.  What I mean is, for example, I open files 1-3, 2-3 and 3-3.  I work on 1-3, save and close it, it disappears and 2-3 moves to the front.  I work on it, save and close, it disappears, 3-3 moves to the front.  Same with it, work on-save-close, but when I close it and it "disappears" there is file 1-3, still open, with the changes and saved but it didn't actually closed, just moved to the back.  I then close it, for real this time, and 2-3 is behind it and 3-3 behind it, also having just moved to the back when I closed it instead of actually closing.  It is causing some workflow issues and confusion with the way we do things.  Any fixes?  Is it a setting or a glitch?  Hope this makes sense and thanks.