Yes I know: Mp3tag i not a filehandler. But it handles them anyhow and simply looses from on eyesight on a simple accounts of moving and does not care about those copied ones
As for copying: it is a little of an overkill as most likely not many users would need that. But if the moving of files should be corrected then I see no problem of taking care also of duplicated files. Giving it as an option would not hurt those uninterested in them but could help the other users
As for moving: that is just illogical or I sense a bug somewhere here. Some times I move a file within Mp3tag and it stays on the list of files and sometimes it does not. I tried figuring that out by moving files that were first played / filtered and / or only to folders in which files already loaded to Mp3tag were- but I could not find a pattern. All in all it should be like this: you move a file to whatever location and it stays on the list no matter what. [And if the file cannot be moved because there already is a file with such name at the destination- then spit a message about it. If such file later cannot be renamed because of the same- spit an error. Just like it is happening right now]