The bug

So on a multiplayer server, if you jump off the ground and then right click on a ridable entity like for example a horse before landing you will get kicked from the server for flying too long and in the server log you will see a message such as:

[17:54:58] [Server thread/WARN]: Jobe was kicked for floating too long!

Code analysis

Based on 1.11.2 decompiled using MCP 9.35 rc1

The server does not reset the field net.minecraft.network.NetHandlerPlayServer.floating when a player starts riding an entity even though it is tracking floating with the field net.minecraft.network.NetHandlerPlayServer.vehicleFloating there and because the floating field can only be set to false by the part of the method net.minecraft.network.NetHandlerPlayServer.processPlayer(CPacketPlayer) which runs if the player is not riding an entity the value remains true.