There are two visual bugs I found with ghasts:

1. A ghast opened its mouth and eyes to shoot at me, but I moved out of its range before it shot. The ghast stopped trying to attack me, but its eyes and mouth were still open as if it was still trying to shoot. It didn't affect gameplay in any way. The ghast continued to move around idly, but its eyes and mouth were still open.
2. On a different occasion, when I shot a ghast with a bow and arrow, the ghast turned to face me, and I moved behind a wall to block its line of sight, When I moved back, it was still facing me, but its body was moving as if it hadn't seen me at all. This made it appear to move backwards, sideways, etc. because it was moving around, but wasn't facing the direction it was supposed to be moving and looking at me instead.