In 1.72 when riding a boat and dragging a horse on a lead your hitbox is on the horse

So I was in a boat dragging a horse by a lead. I had been doing it for awhile (nearly 5 minutes) and made the mistake of getting near a small island with a creeper in it. I swerved far enough away to get out of the creeper's sight range (I only entered his range by 1 or 2 blocks before completing the swerve, then got 8 more blocks out of it) but the creeper was still coming. Not for me, but for my horse! I was fairly sure the horse had enough health to survive (plus he had iron armor on) but the creeper walked right up to him and exploded...AND I DIED INSTEAD OF THE HORSE!!! It should be mentioned that I was definately outside the blast radius (even if I was wrong by a block or 2 I would've only taken 1 heart's worth of damage). Also the horse seemed 3 or so blocks further behind me than usual for the last 2 minutes of the trip. Also I had been exploring new chunks in a straight (diagonal) line on horseback for the past 2 real-world days of gameplay (still only up to x10000 z10000 or so) and experiencing small but constant lag spikes (due I think to the horse's speed vs the need to spawn brand new chunks constantly). Only horseback travel was causing it, and only when exploring new territory. But somehow I think that last one wasn't related (just being careful to include everything).
My guess (and it is that...a GUESS) is that when you are both A) riding a vehicle and B) guiding a horse (in this case via lead rather than horseback) something in the code mistakes those 2 things happening at the same time for proof that you must be on horseback.

Steps to Reproduce:
1. guide a horse with a lead.
2. put a boat on the water and get in
3. find a creeper, making sure you're just out of sight range but your horse is not.
4. Hmmm...do you think me dipping into sight range by a block or 2 was a vital part of it? I'd include that if possible however it seems like it would make it 10 times harder to reproduce exactly.

If it is reproducable that should do it.