There seems to be some of confusion over the difference between the appearance of the "shutter blur/mirror slap" problem and normal motion blur. The first clue is the conditions: the 1/100s region should not cause motion blur with wide angle lenses. Then, the appearance of this problem is very distinctive, and hard to mistake for anything else.
Here is the clearest example I can give from my own K-x and DA 15 ltd (100% crop). Notice the distinct "doubling" of the roof and the bricks, almost as if it were a double exposure.
1/40 s (unblurred):
1/100 s:
If your conditions don't match (~1/80-1/125 s, wide angle lens), and it doesn't look like this, then it is most likely
not the shutter blur/mirror slap problem.
Btw, I have difficulty reproducing the problem indoors at close focus distances. All my shots that display this problem are outside and infinity focus. Don't know if this is a relevant clue.