I know it's been forever, just wanted to check in. Is this still happening? To clarify, are you opening the second copy of the item in a tab separate from the first copy (i.e. you move the first to your vault and without refreshing your inventory, try to move the second copy -- from another tab or opening it from an un-refreshed page)?

Also, moved this into the Site Functionality forum, since I don't think it's a Creative Department type fix.