Quirky problem with Nikon FM - shutter fires when film is advanced

[mfratt]

... about 80% of the time my shutter will fire when I advance film (on the return stroke). It will not do this when the lens is detached.... Help?

 

[Joe Jesus]

Oh my god, I had this same problem with an FM10. I ended up using a different lens, now it no longer happens. It has something to do with the mirror return lever, I think. Thats what I was told, at least.