Basically just what happened on the video. This sometimes happens when driving onto rocks (that should be drivable onto) that are at an angle, plus on railways from what I've been able to reproduce. I don't know whether this happens everytime you go here or onto similar rocks.

When I was about to hit the rock I hit the brakes, but at the moment I hit it i was no longer holding them. That is all i did, I didn't touch the spacebar, just the S button. On the rails it happens totally randomly, and only when driving onto the metal rails, not the wooden planks between.

We should be able to take these bikes into the terrain without having to worry about the bike/character getting launched, and in that killed. Since they handle terrain so well, they should be handling the same on rocks and objects.