I had a similar situation with an artifact, but it wasn't Cocktail. After several failed attempts to exorcise the ghost I had a flashback to an old sovereign remedy I had not had call to use in at least a couple of years, and rebuilt the Launch Services database. Problem solved and the ghost exorcised from the system.

Cocktail, OnyX, TinkerTool System, MacPilot and several other utilities all have a function for rebuilding the Launch Services database.

If we knew what it was we were doing, it wouldn't be called research, would it?

— Albert Einstein