No, it is not a tiny bug... You can't have duplicate IDs. When you have duplicates, the suffix will be added in sequential numbers. I don't know if it was done in Inkscape or FZ. I didn't see duplicated ID names so I am not sure what caused it... It might have been something that you previously had done... You could go back and look at your inkscape XML editor and see how it is labeled.
Don't forget my 
(like this post), if you like... I am collecting them, 
Learn something new everyday... 