If the player places a boat on a slime block or bed and enters or leaves it, the boat will jump, up to 25-32 blocks.
Tested on Win 10 and android.
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is duplicated by 24
relates to 2
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The exact same bug was fixed in java edition. MC-90352 Requesting review.
Reopened for review.

The same happens with beds...

I thought this might be due to the rider's seat position in a boat being -0.2 Y, such that the rider moves downward when mounting. However, nothing changed when I set the seat position to 0.0 Y with a behavior pack. Also, the boat bounces up regardless of whether the player stands several blocks above or below the boat when mounting.

Affects in 1.20.1 & 1.20.20.20 Preview

Affects 1.20.13 Hotfix and 1.20.30.20 Preview
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