Commit
847ad16eed6e4bd05ff32d1383ab0c4db7bf4f98
by md_5
SPIGOT-5562: Entering a boat triggers VehicleExitEvent
This patch prevents entities from riding a vehicle they're already riding on. When trying to enter a boat the client will send up to two packets for each hand causing the server to think they should enter the boat twice, despite the first interaction being sufficient.