Got poisoned while playing with the Biohazard and managed to get a charge off, but it did not deal reduced damage:
http://steamcommunity.com/id/racercowboy/screenshot/595842156906263236?t...
I noticed the normal shots are affected, but not the charge shot. Maybe the charge shots not being affected by gun damage has something to do with it.
That must be it. You're poisoned, but that orbiting bullet is a separate clean entity