Bukkit

What steps will reproduce the problem?
1. Place tracks on two unequal-levelled blocks so it creates a slanted track.
2. Put a sign near/under/over said track and make it a speed multiplier.
2a. I have only tested it while going upwards with the minecart. Also only tested speeds faster then normal.

What is the expected output? What do you see instead?
Expected: Speed multiplying
Instead: Bump into the block and turns around.

What version of the product are you using?
V1.4 for CB 1060

Do you have an error log of what happened?
No

Please provide any additional information below.
I'm running CB 1135 and not the autor's reccommended 1060.

Same experience here.

It's a problem with the engine's collision detection. The minecart goes so fast the engine thinks it has collided with the block the slant was resting on.

This is a know issue, but sadly there is not much to do about it, because , like @animalvgamer said, it is part of the minecraft engine...