I don't know, but it would make more sense to me if the Forum Post Achievements were listed under Social, instead of Basic.

Forums are social. .__.;

I know this is super miniscule and really benefits nobody for me to post this, but.. It just makes more sense..

Hm... that's true xD I never noticed o_O

It's a pointless post, but still. .__. It seems like it is a mistake.

That makes more sense I suppose

I think it is this way because the forum posting achievement came out before there even was a 'Social' category and they were just never moved. You're right though, they would fit well there. :P

I think in general the achievements need a new organization. And yet I have no suggestions on how to do this :P