The bug
Items falling through boats because they aren't completely solid.
How to reproduce
Put a boat in water
Throw any item into the boat
Wait until the bobbing cycle reaches the lowest point
Observe the item fall into the water and then out
Related issues
Attachments
Comments

Dupe/Relates to MC-4 ❓

MC-4 is block edges. This is about boat solidness.
So it's not a duplicate, but it's similar.

It was already marked as related so no need to convince us.
This issue relates to MC-94168.

Confirmed for 1.13.1.
Can confirm in 20w48a.

Can confirm in 1.19.3.