Some K-r users at the Chinese Xitek Pentax forum reported that their K-r had the mirror-jumping disorder shown up if manual K-mount lenses were mounted (but yet no problem with newer AF/digital lenses):-
http://forum.xitek.com/showthread.php?threadid=920594
(See the opening post and the 1st reply by two different posters, whom confirm the same issue, Google English Translation Here)
It seems that this problem is strange enough. As for my own K-r, I have not encountered the same problem with my manual Pentax lenses before. But I did encounter for times that double-shutter firing did happen in *single* frame advance mode and so did it happened with my K-x. Usually, the problem seemed to be related with the ambient temperature as all the times it happened I was shooting outdoor at around 10 Deg. Celsius something. Besides, there was another fault case I encountered which so happened my K-r might have burnt my Sandisk Ultra SD card when I shot more rapidly continuously in a short period of time. Nonetheless, yet fortunately, it has not happened again with my new Sandisk Extreme card and also with my K-r programmed with the later K-r firmware versions 1.10 and now 1.11.
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