The item “Demystifyin’: Tailoring” did not provide any Midnight Tailoring Knowledge, it used the item and removed it from the vendor, without giving me anything.
Occured after using “Demystifyin’: Enchanting”, maybe using both in quick succession caused the tailoring knowledge to not be rewarded.
Adding to this – I also bought the Demystifyin’ Tailoring & Enchanting knowledge items from the renown vendor. The echanting gave 10 knowledge points and the tailoring gave nothing. Reload UI & Relog did not resolve.
Currency was used during purchase and no option to purchase Demystifyin’ Tailoring agian.
Same thing happened to my Jewelcrafter. Used the Demystifyn’: Jewelcrafting, it disappeared from inventory, gave no knowledge, and can no longer buy from vendor.
The book “Demystifyin’: Tailoring,” the book “Demystifyin’: Leatherworking,” and “Demystifyin’: Jewelcrafting” (all sold by the Zul’jarra’s Forces renown vendor) do not correctly award +10 profession knowledge points. These are the only three I bought, and realizing that they weren’t correctly awarding knowledge points, I stopped buying the others. So I can’t confirm whether the other books are working correctly.
A user on WoWhead has reported the same issue with “Demystifyin’: Tailoring” and a user has posted that the Jewelcrafting book doesn’t work. But I can confirm that the leatherworking book did not work either.
My leatherworker, tailor, and jewelcrafter all have a LOT of knowledge points, but obviously that should not make a difference here.
I’m now missing the 750 voidlight marl and 150 moxie it cost to buy the books. I concede that I should’ve held off buying the other two upon realizing that the leatherworking book was bugged.