No, generally I would say that is working as I would expect it to
Looking at the code briefly, there may be a situation where if you previously had 0 banned emails, and then inserted some new ones directly, that the first time a banned email is checked for after that, it may have done an initial rebuild of the cache, but beyond that only deletes and inserts would trigger a rebuild under those circumstances.
From here on out I would just assume that you have to rebuild the cache manually if you ever insert any records manually.