Object going through the floor at high speed

I have a pawn with physics enabled, driven forward by impulse thruster on key press.

I also have a floor that is a Landscape.

When I set the speed at about above 25000 my pawn just goes through the floor at that speed without colliding. It collides faultlessly at all other times - ie if it has not reached max speed. Is this a bug or am I missing something?

I also have this problem.

Did you managed to work it out?