Be careful with your mouth.. xD

Ok this is because you probably had few games left to get to a higher belt.
So when you gain ur higher belt your rank decreases.
The rank depends on how much games you have left.
For example:
You need 1 game to be 6th Dan. = And you could probably be rank 1
*After winning a game
Congratulation your a 6th Dan!! = After some minutes your rank decreases. It depends on the games u need. Rank 2 - Rank 435

This happens to everyone~
I hope u understood.