Prevent Railblock from changing Shape.

Hello, once again I have run out of ideas how to do this:

Im working on a railblock whos RailShape is always ascending, to implement a Rail jump.
The logic to make minecarts actually jump works fine, and when placed the Rail is always ascending away from the player.

However, any time a rail is placed in front of or behind it, it updates and converts into a straight rail.

To solve this, I experimented with the following functions, but without success:

updateState()

neighborChanged()

getRailDirection()

updateShape() and

updateDir().

Nothing I did with any of these functions stopped the rail from actually changing shape.

Does anyone know what I have to do, or at least what part of the code is responsible for this?

If I need to provide more info or my existing code, please let me know.