@cleverest I tried to replicate your issue, but could not. I can bulk edit a group of games (either existing or after new import) and make a change (series, genre, etc...) then click a different file or group of files and edit as well and it does not affect the prior group of files. At least I think I am understanding your issue and tried my best to replicate it.
I was adding new playlists so trying to test this worked out since I was using the bulk edit already.