So when a player presses shift, he would normally unmount the vehicle he is in.
With Protocollib I could cancel the STEER_VEHICLE packet (PacketPlayInSteerVehicle) and it wouldn't unmount.
But with the new 4.5.1 version, the cancelling doesn't work.
It does says its cancelled, but it doesn't stop players from unmounting.

So expected behavior should be stopping the players from unmounting.

Version info:
dump-2020-07-02_14.56.30.txt