After noticing (on SK) that Death March II was never hitting my groupmates, I figured out the reason was that I typically cast it during a fight while having a NPC targeted. I then ran a test and discovered it was not just the spell and this happens with all beneficial group buffs. Cleric's casting Hand of Glory, Enchanters casting True Thoughts.
If /tgb is on, it will attempt to cast the spell on NPC's. The desired effect should be something along the lines of if target == NPC, group spell cast as if self was targeted, instead of trying to cast it on the NPC.
Using SoD client if that matters.