If you ride in a boat and get a few dogs or cats to follow you you will die like I said above. Because they teleport to you and the death message will say ******* fell from a high place.... I have reproduced this several times within a few seconds...
I just had an issue with this bug on my HARDCORE world. I died.
I was riding in a boat and I had about 4 cats that I had bred. I was moving from one location to another and the cats teleport to you as you move. Well one of them hit me in the boat and the boat broke and I instantly died from 'falling' according to the death message on screen.
Luckily I had only about 5 or 6 hours invested into the world thus far...
I am on Minecraft Pre-Release version 1.6.2
Just confirming this is still happening in 14w21b