Lambourne
Ahn'Qiraj Raider
It ain't bugged, you just got lucky. It was bugged at one point in 10man and was 100%, but they fixed that. I got it a couple weeks ago too, but haven't seen it since. Did get a Drake of the South Wind yesterday though. Nothing beats the Rag mount though, it's supposedly the largest mount in the game too. Can't even fit through doors lol.
Yea it could be luck, just happened to be my first ever kill of Ragnaros. And yes, it's enormous, it blocks so much of the screen you can't even see where you're going really.
tbh I was just bored and was checking out some old raids I hadn't seen before. Didn't even know about the mount, nor do I collect them. I farmed Rivendare's and the (nice and compact) Nether Ray back in TBC and have been using those ever since.