Originally posted by matroxication Came across the below thread and looks like Stone G has similar issue with different lens
That thread is an old one and is related to the well documented problem that started with the K10D. Pentax switched to a completely new design of focus screen and that caused metering inaccuracies with manual lenses. I experienced it myself with the K10D. Some lenses were worse than others and it generally manifested itself as a progressive severe overexposure as the lens was stopped down and metered with the green button.
My K1 does not have this problem at all with any manual lens. I have tried the very same lens you have a problem with in both indoor, outdoor ant high contrast scenes, and cannot replicate your problem. As you have only experienced problems with one lens and not your 50mm I can only suggest the lens is at fault.