I have a zombie piglin inside a ghast (both in minecarts) with a snowman throwing snowballs at the piglin to hit the ghast and a trapdoor on the block infront of the snowman to block it's view and switch off the farm. The fire balls are deflected with water jets.

The ghast will fire at the snowman initially but once the trap door is lifted and the view to the snowman blocked before the ghast has a chance to return fire, the ghast will bug out. After the trap door is lowered again and the snowman continues to attack, the animation of the ghast will continue and it will flash red for impact but it will not fire back at all. 

In offline play, to fix this I have to log out and back in but in realms this bug is permanent (which is incredibly annoying because it means having to pull a new ghast from the nether into the overworld on survival). This bug has been seen in creative, survival offline and in realms. Please fix it!