Deleted accounts showing up on site leaderboards

When an old account is deleted (instead of transferred into a new account) the deleted account will remain on the leaderboard. If a new account is created using the same name it appears to show the same account twice (one with the old points and one with the new points). 

The old account does not show up online or in our system.

Depending on the leaderboard the account will either fall off at the end of the year, at the end of 6 months, or at the end of the month.