I think when enemies are killed and don't drop health/ammo, they are only dead on the client. They will still shoot at you and such sometimes. Not sure why only some spells do this, but as of this version explosive spells (like light rocket or flame arc) do this too. Said explosive spells also cause a fatal error. Also, I forgot to mention this unrelated issue (maybe?) but sometimes I'm considered dead when I'm still alive. Like, SRF hack will fail or I'll spam deathnoises on the other players' clients. Same can happen to other people of course. When this happens they turn invisible but I still see their shots.
