I noticed that when using the AH mount, targeting the Auctioneer NPC while opening Imperial Silk Cocoons would not add any attempts. The debug log shows that Rarity is checking for the targeted creature's ID, and not the container item that is being opened, which doesn't net a match (obviously, as the AH NPC is not a relevant one for any items in the DB).

Even weirder: It only occured when I had the AH window open, but not when targeting the NPC without having it open. I need more containers to investigate this behaviour in detail, though...