In my last K-x review, I reported that the K-x is a Shake Addition (!) DSLR as found practically in the field with more blurred pictures were resulted when shot handheld at lower light. Today, I've come across two posts and test demonstrations with comparison pictures posted at the DPR Pentax forum that other K-x users do find similar problem (but of different phenomenons and possible causes, will discuss a bit more below..).
First of all, the OP of the thread below found that his K-m is consistently more stable than his K-x:-
http://forums.dpreview.com/forums/read.asp?forum=1036&message=34327386
He then concluded that it's the serious mirror slap vibration the culprit, as SR can reduce and compensate for the vibration somehow after the SR was turned on, in his test.
Then, in the same thread, another poster reported the "same", just for the Shake Addition tendency of the K-x, but not for the same reason and cause as found:-
http://forums.dpreview.com/forums/read.asp?forum=1036&message=34330249
Interestingly, the second K-x user who posted found that it's the SR the culprit, but not the vigorous mirror slap, if any!
Well, here is the 3rd K-x user who can give his comments, i.e., me! :-) I found that the mirror slap of the K-x is not as gentle as the K-m and actually cause more vibration. I did also find, for times, that the K-x' SR is not as good and effective as the K-m's. But I do not think neither my K-x behaves as extreme as what the above users' K-xes do for both the mirror vibration and the SR (a bug or defective sample?).
While this K-x Shake Addition Issue is yet to be investigated further, it is just so difficult to predict its behaviour(s) and it seems that different units and different samples do vary in an erratic way, which is No Good and actually a really bad thing as there are issues anyway. :-(