by Hydramith » November 20th, 2012, 1:54 pm
Is it known? Yes
Is it a bug? No
Internaly the achievements have been made faction-specific like many other achis before it.
They (Blizzard) already stated that in 5.1 they'll remove the visibility of the other faction's tamer achievement in the UI too. This can't be hotfixed in though, so until a patch (likely 5.1) comes along, we will still see the achievement we won't be able to get for that faction.
The only thing I ain't sure about wether it's a bug or not is being able to actualy battle the other faction's continent grand master battler. By the achievement logic you should only be able to battle either the Kalimdor or EK master, and not both.