it is those curbs, they have no slopes on backslide, so the effect is similar sliding to pedestrian zone which is raised a bit.
I have even experienced what happens when you slide to pedestrian zone which has raised concrete curb with no slope... well your car jumps surprisingly high.
Yeah, had in mind that it would be easier to follow on one car/track, quess i will try to include more tracks for the next time Got that funny jump you did on aston on record too