My PA actually mentioned this to me. "Most people will lose ten pounds plus or minus, but occasionally, you won't lose at all on the pre-surg diet. It doesn't mean you're broken. Don't panic if you don't lose."
My PA is severely type one diabetic, and she, herself, didn't lose anything on the pre-surg diet.
I had the good luck to lose a few pounds on it....but I know there are people who really don't, or who only lose a very minimal amount.
It's ok. You're unusual, but not unheard of:)