Hi
I do not know the K100D but just to through another possible cause into the ring for consideration:
If the cam has a
anti-
aliasing function could this have caused it by way of a software malfunction? (Corrupt file) But then again it's hard to imagine that this malfunctioning software will do this sort of thing intermittently. Still, anything is possible I guess.
Otherwise I think it could be the dreaded self-mutating Mongolian basket weave virus
I hope not otherwise your cam will turn into a basket shopping bag one day. And then it's a basket case. (Sorry for the lousy humor, I can't help it)
Greetings