The damage done to the robot by Professor Robinson with the metal bar is gone after Major West and Dr Smith stand him up from laying on the ground.
When Dr Smith is left alone on the path in the Anti-matter world by the robot, shadows from the tree branches in the foreground can be seen on the fake mountains & sky in the background.
When Will and the Robot enter the anti-matter world and the rocks begin to move towards them, the shadow of a crew member pushing a rock can be seen.
Since matter and anti-matter annihilate one another when they come into contact, a large chunk of the Robinson's planet would have been destroyed as soon as John's duplicate appeared.
Inside the ship the Robot tells Will that the anti Prof. Robinson does not cast a shadow. But immediately afterwards when the anti Robinson goes to the locker to get the metal pipe, he casts a rather pronounced shadow on the wall.