Animals Get Stuck Into Ground When Minecart Is Destroyed When Being Ridden.

I made a roller coaster for mobs to ride in (mainly pigs, cows, ocelots...) but when they all got too close together i stopped the "ride" and destroyed the minecart.
What I expected to happen was the animal would run free
What happened was the animals turned black and sunk into the ground.
How to trigger this bug:
1. Get some kind of mob into the minecart
2. Destroy the minecart
99.5% or the time it does this. Only once or twice it didnt.
And it happens with all texture packs. Default and all.