This could be an intended feature or duplicate but I have just fought the Ender Dragon and at the moment he died, he was hovering right above the original portal that spawns as soon as you enter the End. I saw afterwards that that portal had been overwritten by another one on top of it. Only the top portal has the black voidy bits that you jump into.
Again, I am not too sure if this is an intended feature. I can give move details about the environment and world if needed.