I have noticed something very similar, but in order to avoid posting yet another duplicate thread, I have decided to comment here.
When I close Minecraft (with either the X button or the "Quit Game" button) it continues to stay open. However there are a few key differences in this situation.
1. I can close javaw.exe in the task manager.
2. The process hogs ALL of the available CPU.
#2 is a big problem because it easily overheats my system within a matter of minutes, as well as slow it down greatly.
thank you
ok thank you can you direct me to the report?
I believe that this is a de-sync issue. This means that your boat is not really located where you see it.