The bug
I can ride a boat from so high up and fall down and take no fall damage. The 1.8 boat would make you take fall damage. This needs to be fixed.
Code Analysis / Fix
Code analysis and fix by @unknown can be found in this comment.
Attachments
Comments

This issue relates to MC-98160.

I personally like this issue. So, you're being chased on a mountaintop, and so you put a boat down, hop in, and paddle off the edge of a cliff. You survive, and make an escape. XD

i've only just seen a player on my server use it and thought they were using some sort of cheats at first.
Can confirm for MC 1.12.1.

Confirmed for 1.12.2

Is already marked as affected.

The following is based on a decompiled version of MC 1.12 using mcp940.
Please link this in the description of the report.
In the method net.minecraft.entity.item.EntityBoat.updateFallState() you have a piece of code that will always set the fall distance to 0 if the boat is not on land, its actually just wrong placed in the method.
The piece of code:
if (this.status != EntityBoat.Status.ON_LAND)
{
this.fallDistance = 0.0F;
return;
}
Method with wrong placed:
[media]
Method with right placed:
If this is fixed, MC-98160 will be fixed too.
Hope this kinda helps 🙂

Confirmed in 19w36a

Affects 20w30a

Try falling from 49 or 50 blocks high, if you just hear a big fall sound, press W,A,S or D.
Can confirm in 20w48a.
Can confirm in 21w03a.
Can confirm in 21w05b.
Can confirm in 21w06a.
Video attached.
Can confirm in 21w07a.
Can confirm in 21w16a.

Most likely intentional because MC-119369 has a Mojang Priority.

Can confirm for 1.17

Can confirm in 1.17.1.

Confirmed in 1.17.1.

everyone uses that i think its intended