There is currently a glitch when awarding this mount and faction changing. As of patch 4.2, faction changing from one faction to the other will award this mount despite having used the first mount on your character earlier.
So, for example:
1. You receive this mount for 75 battleground wins as Horde
2. You use the mount, learning it and adding it to your collection
3. You faction change to Alliance. You now have the Alliance version learned in your collection
4. You also receive a second account-bound alliance version of this mount in the mail, even though you've only won 75 battlegrounds (not 150 yet)
Note that the mount is account bound and can be sent across faction. The mount will also change depending on what faction the receiver is (so you can send it to an alliance alt from horde side, and it will change into an account bound alliance version.