Please make sure you've actually got all of them as when testing we found it works correctly, but displays wrong number of achievements.
In case - this thread is about this as well:
viewtopic.php?f=4&t=141&p=557&sid=f9aa48cb047a5cdaff98c3e82e54befe#p557thanks
EDIT - in case it is bug indeed, we're gonna fix that, but please be patient, it's hard to track the issue and find whether it is caused by the game or by Steamworks.