jagged stag
When your inventory is full, completing a quest will cause you to throw the quest rewards forward.
In this case, the quest items went past the quest giver into a house that doesn't seem to be accessible through normal means. My friend lost out on a gun reward because he couldn't get to it. I also picked up his 10 letters of favor.
The area behind the NPC can't be accessed and although i can no longer see the gun that was on the ground, neither of us picked it up and is seemingly lost.
dreamy sun
Thanks for the report, its a known issue, it will be fixed in one of the nearest updates.