Hi! I've noticed how strange minecarts act in 1.9.x . When you place down a minecart standing still, you can throw snowballs SOMETIMES as it is random. When riding a minecart you cant throw snowballs at all. This is very important to me as to a lot of other people for example using it in a gold farm to agro pigmen, so i hope you do notice this and hopefully fix it in the future updates.
Duplicate of MC-96588, if you have not, please use the search function in the future, to see if your issue has already been reported.