Blimey! - thought I was talking to myself out here in mediocre land... You don't have Morgan Freedman sitting in front of a huge curved panel of screens, muttering "but this is unethical PMDman - I will only do this once!"
Sorry - just been to see 'The Dark Knight'.
You are almost certainly correct btw.
But I have done other runs where the rhythm is better and more drive is generated off the end of the U (kinetic - potential - kinetic energy); and we know that the BoD physics engine is a little susceptible under stress.
Also, it's poss to do this without the flip off the Y and get more drive.
I have been discovered by my 12 year old daughter and labeled 'SAD'.
Actually - I went to a magical double bill the other weekend... Dark Knight... followed by... Kung Fu Panda.
What an interesting counterpoise of ideas, style and story telling that was!!! - highly recommended.
PS - this trick might have worked if you had slapped your front wheel down hard right on the top right corner of the "U" - the BOD Physics engine does have a tendency to transfer the speed into a dramatically differrent direction when things like that happen.