Order Results By – Sorting error

Hello,
I am trying to sort listings by average score (using WP-PostRating plugin and sorting feature from General Setup panel).
The score range is 0 to 10.
For some reason the sorting doesn’t recognize double digits and sees the score “10” as “1”. So the scores go like that : 9, 7.5, 6.2, 4.5, 10, 0.5, 0.

Does anyone know how to fix this error ?

Thanks.