Two different K-5 users have reported that their K-5 are having the mirror in sudden movement without any reason and that the disorder does happen intermittently and is unpredictable:-
http://www.dchome.net/viewthread.php?tid=1018474&extra=page%3D1&page=1
(in Chinese, Google English Translation Here)
http://www.dchome.net/viewthread.php?tid=1010498&extra=page%3D1&page=1
(in Chinese, Google English Translation Here)
But the most unfortunate thing is that it seems that Pentax has been unable to pinpoint the cause of the issue and the affected users have both reported that the same problem persists even after repair even parts have been replaced. Let's see what the stories continue, I shall keep an eye on the cases.
Update: Thanks to Blog Reader Gow, we have this video, which shows more clearly the problem and what happens when a K-5 is affected:-
(URL: http://youtu.be/IIQ01XfG3QE)
Update 2 (5-20): This issue has been discussed widely at different Pentax forums after I made this post. Some people suspected that it is the hot weather and just higher ambient temperature that has caused the problem! Well, it looks somehow sensible for this explanation as now it's the Summer and the K-5 in the above video is at Thailand! :-o ;-D
Related:-
The K-5 Have Got a Cold! :-o