The bug
The required space when placing a boat is too small.
This allows the collision box of the boat to intersect with blocks.
At 18w31a will make the boat fall into the void.
Video:
https://www.youtube.com/watch?v=MlRPQVz-y9Y
How to reproduce
Put a boat in your hand
Place a block on the ground
Look at the ground right in front of the placed block
Hold right click while slowly moving the cursor away from the block
Code analysis
Based on 1.12.2 decompiled using MCP 9.40
The method net.minecraft.item.ItemBoat.onItemRightClick(World, EntityPlayer, EnumHand)
decreases the collision box size when it tests for no collisions:
if (!worldIn.getCollisionBoxes(entityboat, entityboat.getEntityBoundingBox().grow(-0.1D)).isEmpty())
{
return new ActionResult<ItemStack>(EnumActionResult.FAIL, itemstack);
}
Linked issues
is duplicated by
Attachments
Comments

Can confirm in 21w03a.
Can confirm in 21w05a.
Can confirm in 21w05b.
Can confirm in 21w06a.
I've attached an updated video since the previous one is quite outdated.
Can confirm in 21w07a.
Can confirm in 21w11a.
Can confirm in 21w13a.
Can confirm in 21w14a.
Can confirm in 21w15a.
Can confirm in 21w16a.
Can confirm in 1.17.
Related to MC-1310.