Rank facebook return wrong

Question

The ranking list on the server has 2 users:

A: Rank 1, score 5 (Update at 5 PM)

B: Rank 2, score 5 (Update at 4 PM)

 

Using GetTopNRankersFromFacebook () returns the result wrong

B: Rank 1. score 5

A: Rank 2, score 5

 

if using GetUserRanking(A) return  A:rank 1

 

Why when using GetTopNRankersFromFacebook () returns the wrong ranking order when 2 users have equal score, thanks