Disposing of corpses breaks quests
This bug occurs on Windows 10 (64-bit), OpenMW version 0.40.0 (64-bit), Steam Version, English, with only expansions installed and selected.
During the quest Larrius Varro Tells a Little Story, if the player disposes of any of the corpses of the Camonna Tong members in the Council Club the quest giver will no longer recognize the quest as being complete after the "blood bath". If the player does not dispose of any corpses it works as intended. In vanilla morrowind, the quest can be completed even after disposing of one or more of their corpses.
The same bug does not appear to effect Morag Tong assassination quests, perhaps due to there being a quest stage update on the death of the NPC, not a check for dead NPCS and no related quest stage for their deaths prior to returning to the quest giver.