It never used to happen, but yeah it does all the time now. Make sure you always correct it by signing out and back in whilst in the game before going for an achievement. I was going for my 30 wins whilst it said 0GS and it did not unlock. Once I did the sign out/sign in trick, had to win another game to get it to unlock.
Would hate for someone to complete the Perfect World Champion requirements but not get the achievement they deserve.
Done with achievements.