I agree there's definitely a memory leak when you are updating metadata/artwork. I have to exit out of the Mezzmo app, rarely it crashes on its own,...
You could also select to sort the files by Release Date and this would put them in the correct order without the need to put 01, 02, etc in the file...
This sounds alot like the "bug" that I've seen frequently where it thinks that the item, despite the file extension, is a folder, but you can't edit...