Originally Posted by Lowell Goudge 
is it possible that you have a bad contact between camera and lens? If it is hunting like this it suggests that the data for focusing distance is not being fed back to the body as it should.
check and clean the furthest contact away from the lens locking pin, use a pink or gum erasor, not abrasive.
Maybe, but unlikely, I guess. It might be that the new firmware is not fully compatible with some different versions of the hardware including the body and/or lens.
My advice is if problem persists, just contact the Pentax UK's for servicing or technical support. I think his lens and body are both under warranty.
Sometimes those firmware upgrades could create new problems, so if it is not really needed, don't do the upgrades.