Zombie Horse texture isn't showing up & middileclicking them

When you spawn in a zombie horse you will notice that the zombie horse texture doesn't show up at all (or maybe the model doesn't work properly) and when you middleclick the (currently invisible) zombie horse it gives you the regular zombie spawnegg instead of the zombie horse one.
EDIT: when you spawn zombie horses, leave your world and rejoin the zombie horses transform into regular zombies too.