Hasselblad aperture/shutter speed cross coupling problem

Hello, I recently came into a bit of Hasselblad kit -- a 500 C/M and three C lenses. I understand that by default these lenses lock the aperture and shutter speed together to simplify shifting settings without changing exposure. My problem is then even when I press down the little metal tab behind the aperture ring (not the one by flash sync settings, the other one) the rings remain locked together: I can't turn them independently. I'd think I had a mechanical problem except that all three lenses (black 80 2.8, chrome 150 4, and 250 5.6) all show the exact same behavior. Does anyone have any suggestions about what I might be doing wrong?

Thanks in advance.

The manual for the 500c is here.

OK, now I feel stupid. Thank you. I'd looked up the C/M manual but the lens depicted in it was different from mine. For anyone else who has this problem, the interlock release is *not* the little tab that you can press into the lens. It's the larger, ridged flat tab, which you pull towards the camera. This feels weird because the ring on which it's mounted will kind of flex, but it's apparently how it's done.