Hi Craig,
Yes I have had problems with the aperture ring on an SLR magic lens.
I received one brand new from Hong Kong. I was really pleased but as soon as I tried it out I realised it was defective.
I closed the iris down and it sprung back open a bit.
I think I only closed it down twice saw it move back open then looked into the lens and could see all the coating shredding off the aperture blades.
I sent it back and got a replacement.
Craig you should take the lens off the camera and look inside the lens in a well lit room to see if you can see the aperture blades move when you rotate the iris ring. If the iris blades don't move, the aperture doesn't get bigger or smaller, when you turn the aperture ring something is very wrong and you should send it back.