Someone has discovered how to test the K-5 mirror disorder recently, see:-
http://www.dchome.net/viewthread.php?tid=1018474&page=5#pid12074082
(in Chinese)
It is told that put the camera in M exposure mode, then push the shutter speed to the highest, i.e., 1/8000s, shoot in continuous frame "advance" mode for shots in a chain for a while. That's it! If your camera had the illness hidden, it will become crazy after the test! :-o