My Lynx took a knock on holiday, and subsequently I got the same issue - it's quite annoying. I also find that the aperture ring sometimes moves with the shutter speed ring - almost like they are linked together like the Ministers are !!
Anyway, I took the lens assembly apart (done it lots of times, sadly) and I can't see why this is happening - the castellated (sp?) nut is held in place by the cut screw, so the whole assembly should keep still. It's for another day - I'm living with it at the moment, but it would be nice to fix.