When mounted on a vehicle, if you throw an ender pearl, it'll use the pearl and damage you like normal, but you'll immediately be teleported back onto your vehicle instead of your destination. (Or rather, you're teleported to your destination, but then immediately moved back onto your vehicle one tick later.) I've tested this with boats, minecarts, and horses, but I'd guess it happens with any mounts.

What I'd expect to happen: either you'd get teleported to the destination and stay there (off your mount, like a normal ender pearl throw), or you wouldn't be able to throw an ender pearl while mounted, or (at least) you wouldn't take fall damage from the pearl since you're not teleporting anyway.

To reproduce:

1) Mount anything--a horse, a boat, a minecart, etc.
2) Throw an ender pearl.