So I have a few D-lenses. I always set the tab to the widest possible aperture, then control the aperture on the body (D90) in manual mode. Well, the tab on the 200mm f/4 unlocked, and now when I try to lock it back down it will give me f/4.8 and nothing wider. If I try to set it to f/4 the tab will not physically lock. I apply a fair amount of pressure to it, but obviously I don't want to brutally force it, lest I actually snap the tab off completely or some such.
Ironically, in demonstrating the issue to a non-photographer who is mechanically "handy" I showed him how "easy" it was to set the 50mm 1.4D to 1.4--now that won't give me anything wider than f/2! So I've got two lenses that I cannot get to wide-open.
I feel rather silly. Ok. Totally stupid.