I've have this problem with AC 13-14 on several different machines on several different installations. When I open the Library Manager and add a library, if I open the add library dialog again, I will be up one level in the folder hierarchy.
With my strategy of library management, this is a minor but very frustrating quirk. Every time I add libraries I have to re-drill back to where I need to go (which includes scrolling and looking for the folder name). And I can not see any obvious reason for this so it more than likely it's a bug.
