What it says on the tin.
If you are driving a boat, switch seats (while moving), and the boat will continue as if you were still driving. EG, if you are driving straight forward at max speed, the boat will continue driving forward at max speed. If you are turning, the boat will go around in a circle until you switch back to the driver's seat and stop it.
This bug works on all boars that I've tested. It does not affect land vehicles. However, this DOES apply the Marshall and Marid while they are in the water. This also happens if you eject from the boat. It will continue to drive off into the distance with no driver.
Mass closing ancient tickets with no activity for > 12 months; assume fixed or too trivial.
If this issue is still relevant in current dev build, please re-post.
Also note that setting a ticket to private is not the best idea, because hardly anyone will see it.