Hey everyone. I have a 6D with 24-105L IS and was filming a behind the scenes video for a commercial yesterday. I was using a Manfrotto video fluid head monopod focusing with my left hand. Because this was run and gun documentary style filming, I was rack focusing by setting focus at my end point and then putting my fingers on the very top of the lens, turning the ring to rack, then trying to go back to the top to hit my original focus point. What I found was that each time I tried to do this, the ring shifted, and my focus point was a good 1/4" or more out, so that my fingers were no longer at the top of the lens. Baffled, I tried it several times with the same result. If I did not reset, and kept finding focus on the object, rack and try to go back, my fingers would end up near the bottom of the lens. Obviously the manual focus ring is slipping, which means there is no way for me to hit marks with this lens. I haven't had it that long, so I'm thinking it needs to go back. The faster I turn it, the more it slips. I have never had this problem with other Canon lenses, L or not. Anyone else have this issue?