I actually posted about an off-by-101/1 bug on MSO a week ago:

http://meta.stackoverflow.com/questions/212471/how-come-my-association-bonus-didnt-count-towards-the-league-but-someone-else

Tim Stone speculates that:

> maybe it's a race condition where sometimes the association bonus is recorded microseconds before your account creation date and that messes things up

Up to now though, the bug hasn't been answered.