Apparently there has been an issue with the way armoured Nether Drakes have been awarded, as in a bugged issue. Aeus from Blizzard made the following announcement today about the situation.

Following the last maintenance, we became aware of the fact that a larger number of players received the Armoured Nether Drake mount award than was intended. We began investigating the cause of this issue immediately, and have now isolated where it occurred.

Tomorrow morning at 05:00 CEST we will be bringing down all realms for approximately three hours in order to resolve the situation.

As a result of this update, we will first remove all Armoured Nether Drake mounts, after which we will resend Armoured Nether Drake mounts to only those players who should have received them.

We apologize for the confusion caused by this issue. It is our intention to preserve the rarity and prestige of the Armoured Nether Drake mount award, and we thank all Arena PVP participants for their understanding.