The symptoms of windows shrinking this way indicate that a change in resolution occurred. When the resolution is set or changed to lower, the windows are shifted around and shrunk to fit that resolution. Either that or a person could lose access to them and have to reset their postition because it opens off screen (We had that before also) when in low res.
Screen savers or the log-in screen can exist at a lower resolution can cause this problem. In windows 7 the log-in screen can match the res of the desktop under normal/proper operation, so check for the screensaver issue first.
Test first by doing lock with "None" screensaver, and see if it still happens. Try and get the screensaver to match the resolution or find one that does?