What I expected to happen was...
When I happened to jump on top of the boat, I will be able to move normally, like I was only standing on to something.
What happened was...
I jumped on top of the boat (but not riding on it), then when I move in sideways, I tend to shake and move slower (without pressing the sneak button).
Steps to Reproduce:
you may refer to the attached video/file
In case the video will not play...
Place the boat to any water surface.
Jump onto the boat, and no right clicking on it.
Move in any direction.
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Thank you for your report!
We're actually already tracking this issue in MC-156980, so I resolved and linked this ticket as a duplicate.
If you would like to add a vote and any extra information to the main ticket it would be appreciated.
If you haven't already, you might like to make use of the search feature in the future to see if the issue has already been reported.

My apologies, I thought I already have searched enough regarding the issue. Thank you very much for letting me know. I'll search even further next time.