Snowballs do not play attack animation

System.getProperty('os.name') == 'Linux'
System.getProperty('os.version') == '3.13.0-35-generic'
System.getProperty('os.arch') == 'amd64'
System.getProperty('java.version') == '1.7.0_67'
System.getProperty('java.vendor') == 'Oracle Corporation'
System.getProperty('sun.arch.data.model') == '64'

When a player fires a snowball and it hits another player the attack animation does not play (ie. the play turning red and getting thrown back) and the player is not thrown back. However, if I use Spigot and modify the amount of damage a snowball does, the new amount of damage is still applied.