The joint parameters (JPs) got messed up a bit. Select the collar and go to Window: Joint Editor. You'll have to play with the settings a bit to get it to work right. My guess is that the Bend Falloff sphere needs to be adjusted slightly. I'm almost a newbie with JPs so I can't be more specific than that. Once thing I'd try is loading V2 and your hybrid into the scene at the same time and see if there's any difference in location between the two meshes. P5 was a bear for me - it kept subtly moving V3 around which seriously hosed up the JPs. I gave up and went to PPP and it worked perfectly the first time. I had to adjust the JP's slightly with my AnimeM3 because the head was higher up than in the original mesh so the neck kept breaking apart until I fixed the JPs accordingly to include the neck. Hope this helps, Cres