Cresting a hill or entering a dip too fast will cause the mouse to eject, so this is expected behavior. I designed much of the game to try and create teachable moments that apply to other coaster-building games. There are much more trivial ways to buck the mouse, so I don't think it's a big deal.
The booster code is only run by the coaster car, and only when it's in "tracked movement" mode, so it won't affect the mouse. I did notice you can get fairly creative with guiding the mouse around post-ejection. The physical track sliding code might still have some determinism issues due to the physics engine sometimes returning collisions in a different order, but I have an idea on how to solve that. It's something I'd like to tackle in a future update. I could also tweak the mouse movement more extensively, and you have some cute ideas, but I'm also trying to be careful about not breaking existing track designs.
Adding an extra pred would require some refactoring. It sounds fun though, so I'll definitely consider it.