I have a stack of four images: the original, a copy edited in Photoshop and two virtual copies. One of the virtual copies is on top of the stack. If I try to move it to another folder, I get the error "All the selected photos are virtual copies. Only Master files can be moved to another folder. If I make one of the Master files the top one of the stack or if I expand the stack, it works fine. It this a bug? It's super frustrating!