I've interacted with his coffin, both post-Evelyn, and post-Church... nothing.

It's not named quests that don't display (Empty) it's any container containing quest items/handcraftedly placed items. Including, say, the corpse at the start.
Originally Posted by Rainer
the item is not gone, if you trade again with your other character those items are there for you and that's what I find disturbing - the vendor "knows" which person he trades with and has different items for each char

Not my experience. If A trades, then B trades, if I returned with A, he had the same inventory as with B. If C interacts, again I noticed A and B had C's inventory.