What I expected to happen
Nothing really, I just jumped while fishing because I was bored..

What actually happened
I died because apparently I "fell from a high place" even though I was on a boat.

Steps to reproduce
1 Place any boat on water (didn't check for other blocks, probably still works there)
2 Get on (not in!) the boat
3 Jump
4 Stop

This bug was actually hilarious to find, I laughed hard!