@capnm - yeah I do the same thing for the same reasons, and yeah they are a pain to remove. It has you cursing the teeny tiny identifiers textbox in the Edit Metadata dialog when you edit them one by one and try to find the right place in the very long line to chop them out of
I tend to use the tag browser, click on them one at a time to bring up the matching set of books for that identifier and then do the edit as you say.
I know there is limited space on that dialog, but they are the sort of data that you want in a list to easily click on an X to delete etc, dunno how it would fit in though without making it a popup.