Move entry instead of copy

I want to organize my references. So I made subfolders. When I drag and drop the refs to the subfolder a copy in the subfolder is generated. However, I would like to have only one copy. How can I MOVE an entry instead of copying it?

A reference can be in multiple folders. So if you drag it to another folder or subfolder it will remain in the original place and also in the new place.

You can remove the item from the folder by hovering of the folder name and clicking the “X”.

A faster solution is using the “Folder” toolbar button and uncheck and check the relevant folders. That will do it in one operation.