I'm guessing your on a windows system?
That was a bug in photoshop 13.0 where if one had the windows taskbar on the top or left side of the screen, the
floating document windows would stick to the left side of the screen.
If you move the windows taskbar to the bottom of the screen it should stop.
The solution would be to update photoshop cs6 by going to Help>Updates from within photoshop or Bridge.
That problem was fixed in an update.