The metal shelter, which the 3 red robots get blown up in, disappears and reappears in subsequent shots.
When Yosemite Sam is in the indestructible robot machine, Bugs Bunny rivets the top closed after dropping in a stick of lit dynamite.
Yosemite Sam almost gets all 4 rivets loose, but one rivet remains stuck when the robot blows up.
As the robot rides up the ramp of the UFO, all the rivets are now gone.
Yosemite Sam watches the actions of his robots thru a TV monitor even though he never set up any cameras to view such activities.