Trouble with TAMRON Adaptall -2 lens and camera

I was given a CONTAX RTS II Quartz and a Yashica FR-1 then an Olympus OM10 that I gave away as I had an OM2n from my Son but with the OM10 was a TAMRON 'Adaptall -2 135mm f2.5 close-focus 18* BBAR MC with OM Mount so I KEPT the lens and put the 'Adaptall -2 CONTAX/YASHICA mount on it -- now I find it stops down OK when on the Yashica FR-1 BUT when on the Contax it will not stop down !! Any ideas from you Tamron experts ?

I used to have a bunch of Contax gear, and always had the same issue as you with after market lenses. I think the actuating pawl in the camera body isn't quite long enough to reach the tab on the lens mount. I could be wrong though, it's been years since I owned the Contax.