what you have there is sensor split. I actually have a thread here in the forums on the issue.
My sensor also had this issue. I sent it to pentax and they upgraded the firmware. For whatever reason that seemed to have taken care of the issue. I can no longer reproduce it....but if it comes back up its going back for a sensor replacement. Funny thing is, the shot i noticed my sensor split issue was also taken at Valley View in Yosemite. I noticed it while doing a black and white conversion of this picture:
http://www.flickr.com/photos/14288454@N07/5498274600/
Also what ISO are those shots taken at?