Still confirmed for 1.9 release. Need a 2 block distance above the Minecart to throw a snowball out of it or it will instantly break. dose not work if you have only a one block space with a block above you.
This is also happening with mine carts as well in the 1.9 update. Also eggs can not be thrown from horses either.
Named aggressive Pigmen dose not make new spawn Pigmen aggressive even if they are withing the range. My gold farm which used to work indefenetly now only works 2-3 times before I have to re-hit the named pigmen and re aggro everyone.