The 1-1 world demo was released on C64 and distributed with Zzap!. I remember from the demo it ended once you had beaten the stomping robot (the one with the falling pikes in the cave). Yes, you could access other parts of the level in a specific way. I remember I turned into a gyroscope (spinning wheel), heavily bounced into walls and all of a sudden moved through solid rock to a higher level which let me access the last part of the level.
I loved this 'bug'.