I think it's a buggy release. I can't get LR6 to upgrade my old catalog without crashing. I spent several hours on the phone yesterday with Adobe support to no avail. They did discover that by creating a new user profile, LR6 will work properly. But I would have to reimport all my photos and switch back and forth to that profile. Crazymaking. So I think that means the current release doesn't play nice with user settings in Windows. They suggested I contact Microsoft for a solution. I'd rather poke my eye out. I'll use LR5 in the meantime. Maybe they'll publish a fix eventually. This does sound somewhat similar to the problems you've been having RM, but I don't know enough to know for sure.