As iceeagle said.
I just got exalted with [faction=1269] yesterday and completed the exalted quest chain (starting with The Might of Three). I had a problem with not getting the 'The Golden Gate' portion of the Eternally in the Vale achievement, but left it alone because I thought there might be something else I needed to do, or a hotfix coming at some point, but once I was done and had all the other requirements, still no achievement.
A ticket in to Blizz (queue said I had a 2 day, 5 hour wait, but it was answered in just over a day - hurray!) and a chat with a GM revealed that it is in fact a known bug and they are working on a fix for it (the GM also mentioned that they, too, had the same error with the achievement, so he/she felt the pain). Hopefully, they said, it will be corrected shortly and granted to everyone who is exalted and completed every step of the requirements.
I suppose all we can do until then is wait and keep an eye on the PTR notes. *shrug*