Do not mind the numbers appended at the end of each name (song.iso;1 etc.). That is just MC's way of distinguishing different tracks in the same file.
Maybe you are trying to rename instead of moving to a different folder?
I just tried again. Filename change is ignored. I am not sure if this was done for a reason. Other than that, all works.
Using F6 tool, I can move the file to a different folder.
I also tried deleting the file from MC library, as you did, and moving the file in Windows Explorer, including renaming the file name, and then re-importing it. It works.