This is intentional for creative players
This is Intentional I believe. What is happening is when you pick up the exp it goes transparent. If you pick up an item it does the same. I believe it is for people who can have seizures by repeated drastic changes in light. Which is why they made it so you pick up the exp at your feet.
If I am understanding what you are saying.
The Structure void is supposed to be used in place of air when saving structures so that when the structure loads it will always be an air block. If you save an air block in a structure that can be replaced with any block in the world generation.