Yep, I tried my 2.8 Elmar on my M3, and got the same thing. It does not really foul on the cam follower, but it does rub slightly. Looks like the thing to do is to rotate the barrel until it just releases; then collapse without further rotation. Hopefully it can't really do damage, though, or Leitz would have noticed!
“There is hardly anything in the world that some man cannot make a little worse and sell a little cheaper, and the people who consider price only are this man's lawful prey.”