I didn’t see anything anywhere so I apologize if it was posted before.
There seems to be an issue in WvW regarding the capture credit for Keeps and Stonemist not only for the Season 1 achievements, but the WvW category as well.
For example, since the WvW Season began, I have captured Stonemist 5 times, but only received credit for 2 in the “Castles in the Air” and “King of the Castle”. Capturing of the castle includes helping assault both outer and inner doors + taking down the lord in the middle / standing in the circle. The same issue has occurred for “The Keep is the Thing” as well.
I believe this issue is the same issue that happened with the kill credit on the Halloween bosses in the labyrinth. Even though you receive the gold medal, you do not get credit towards the achievement.