No, I have not had the same experience, while having made 6000+ photos with my K-7. However.....
I have seen the opposite effect though: almost complete white pictures.
It took me some time to find the cause: the AEL button.
Sometimes, when taking the camera out of the bag in a hurry with a long lens attached I do everything in one move:
Take the camera out, switch it on at the same time.
However, to hold the camera I'm having my thumb (accidently) on the AEL button and the lens cap is still on the lens!
My thumb is needed on the camera to take it out with the large lens on, and I'm sometimes more focussed on the subject than on what I'm doing with the camera.
Then, when I take the photo within 30 secs, the exposure is still set to complete darkness
resulting in an overexposed photo by far!
Perhaps, your problem is the result of some sort of user action as well....
- Bert