What is going on?

The only reason that would happen from what I have heard is if some people keep rating your discussion negative but it would take more then just one negative.

It sounds like you had a negative rating on one of your posts! Have you made any posts lately that you think other users may not have liked? Luckily your star can go back up to a 10! Just keep posting and being helpful and other users should start positively rating you to get your blue star back!

For my experience When i reach 100 post, my star rating is number 7, and the feeling of it for me are very much happy, then i notice one day that my rating is turning 8, when i read your discussion, before i had an idea that if you rate 1 in your star you are the highest, i open and try to comment on your discussion, but before that i read the two comment for you, and i realize that i get 1 higher good rating for me, for you gudluck and pursue that the 10 star that you reach will back to you soon.