Unable to throw snowballs outside of player and/or minecart hitbox only after cart is moving. When first entering the minecart, player can throw snowballs without issue.
Linked issues
Comments

But duplicate of MC-96588
Unable to throw snowballs outside of player and/or minecart hitbox only after cart is moving. When first entering the minecart, player can throw snowballs without issue.
But duplicate of MC-96588
Cortus
(Unassigned)
Unconfirmed
Minecraft 1.9
Retrieved
Similar to Issue MC-88934