I purchased the Biogon about a month ago, gray market, and I've noticed that, although it gives me no problems, I'm unable to lock it into place when I mount it on my G-1. The 45 Planar locks in with no problems, but the 28 won't full "click" and I can take it right off. I'm worried this might produce light leaks or something. Didn't have this problem with it when I first used it, and lens was brand new. Any suggestions?