Sound like a rights issue. MediaMonkey may not have rights to remove the originals once the files are moved.

If you move files outside of MediaMonkey the originals become Dead Links. You need to either use File > Locate Moved/Missing Files before scanning the new copies or remove the old copies from MediaMonkey.

I copied a lot of albums from my PC to an external hard drive after supplying each with a cover pic. Now suddenly the last one of these albums refuses to co-operate. It does not show the pics on the HD and also copies each track twice. The big idea was to just delete each double version but when I enter ok, all the tracks have vanished, the album has vanished. I tried to outwit the system by just copying the single tracks into another folder on my PC to move them to the HD with a file manager, but even here each track drawn from MM exists twofold. ??? Thanks.