F5 canceling W/ minecarts + slime blocks

F5 mode get's canceled when you are riding in a minecart and get pushed by sticky piston+slime block.

What I expected to happen was that I would just stay in F5 mode.

What actually happened was that as soon as I was pushed by the pistons, I went out of F5 mode.

Steps to Reproduce:
I just built the thing shown in the attached files.