'forum topics answered' achievement bug

The achievement 'forum topics answered' bugs at my account. The achievement tracker says I've posted two answers at a (random) topic, which is correct. I' ve only posted two, but I've got the achievement that I already posted 5 of them.  It's not accurate. Of course, it is really nice to get an achievement, but I think this is not the right way of earning them. (WoP NL)