Instant death when boat hits mob

While traveling in a boat in water 1 cube deep, I hit a squid and instantly died. Just

dead. The cursor would not move to select respawn without exiting full screen. A short while later, I was traveling in a boat, and I think one of my dogs teleported to right in front of the boat and

instant death. This time the water was very deep. There was no warning that the health was dropping. I went from full health to dead instantly.