When you choose no platform in world creation, you will spawn falling into the void, go ahead and fly upwards to escape the void and another sun will be revealed. Also, when going down to the void the clouds turn black. And last but not least, when you stare at the 2nd sun and go down to the void, the void turns the 2nd sun into the moon.

How to reproduce

Start by choosing air as you're platform in world creation.

Then choose creative mode to fly.

Then try going down to the void, it will turn the clouds black, and once you go upwards a 2nd sun will be revealed, and the 2nd sun will turn into the moon if you go back to the void.

Observation

Going down to the void will turn the clouds black, and once you go upwards a 2nd sun will be revealed, and the second sun will turn into the moon if you go back to the void.

Expectations 

There should be no second sun, and the clouds shouldn't turn black even if you are nearby the void and the sun should never turn into the moon.