inventory is not always removed when it has to.

[passer-by]

That would indicate that you have the coat twice in your inventory (as a single item).
Do you directly add the inv item via a dialog script command or do you do it via dialog_request?

I don't use dialog_request

friend: Well, if that's the way it is...can you make some coffee?
ego: Sure. Give me your coat.
add-inv 18
option-off 3

It seems that somehow I add the item twice, but I can't remember how. So I put

//script for hotspot12: Use inventory on hotspot
LoseInventoryFromCharacter(EGO,18);
LoseInventoryFromCharacter(EGO,18);

and it worked...