There's the bug you already know about: when your horse dies in water, you appear to be sitting in third person mode.
I discovered another problem: whenever you throw blocks after your horse drowns, the items come from where your horse died. And you cannot pick up drops, although I did pick up a few things when the horse drowned, I think because for item dropping/picking up purposes, minecraft thinks you're still on the dead horse.
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In the little circle you can see the sand being thrown from empty water, in the general area where the horse died, despite the fact that I am clearly in the foreground.