Bug in registration of M18 weekly mythical key to M9 loot chest

[Digimongg]

WoW Freakz link: https://www.wow-freakz.com/item_finder.php?item=138019&name=mythic-keystone
Bug description:
-Good day, What happens is that: Today 10/17/2019 Thursday, With my character: "Lycanrocfuta", at the time of receiving my item from the weekly chest, I had as record an m18 key in Neltharion Lair ( proof) , but when seeing the loot, gave me an Item level 900 (proof) Forged by the Titans "M9" and apart from the item and the AP, an M8 Neltharion key.
-I don't know what would have happened but that is what I claim in case it was a bug or registration error.
-I do not have a proof (image) of the record of my m18 key but as I saw it is still in the list of my Guild records, or I don't know if it is possible to check them from the system that posted that record.

Thank you

Proof: https:https://imgur.com/a/yMlap8w