Guild Wars 2

The boss achievement “Cleanup Crew” is supposed to be obtained by “Defeat the misplaced steam ogre” event. But there’s no achievement get after I kill the ogre boss and open the chest. I also tried to re-login the game but still nothing happened.

Is this a bug or just I missed any step?

I solved the events again, and got the achievement this time. Don’t know whats going on with the first time, however