Originally posted by Lowell Goudge just a simple guess here, but I am willing to bet the lens mount is either painted black or black anodizing.
Some bodies, the K7 being the one I own that does this, need the pin furthest away from the lens locking pin shorted to the lens mount to permit aperture activation.
I have a set of Vivitar Automatic extension tubes, and note these are old and the term "automatic" means simply they control aperture by stopping the lens down to the aperture ring setting, as well as having the aperture coupling to the body for TTL metering. It has nothing to do with the PKA mount and the electrical transfer of aperture information to the body, or body controlled aperture.
if you clean the paint off the mount in the area of the contact pins it will work
Fair enough. They appear the same as I have, and mine are black anodized at the mounts.
So, scraping off paint it is.
Still, why does it work normally on older bodies, and why the need for suddenly putting this "feature" into effect? That's what generally puzzles me.
In any case, thank you, everyone, for your replies.