As you can see in the attachment, there's a white thing resembling an end portal. I don't know what it is but it's not supposed to happen(I suppose)

Steps to trigger the bug
1. Start a superflat world
2. Kill two withers (making them, not with /summon)(In the OverWorld)
3. Summon two Enderdragons in the Overworld and kill them
4. Make a 1x1 tower to one of the End portals
4b. Enter the portal
5.Destroy some of the crystals with ender pearls
6. /summon two Withers and kill them
7. kill the Enderdragon
8. With TMI, make a Jump boost IV potion
9. Jump around
10, look for the thing (it can be purple and black or white as shown in the picture and can sometimes can fly and cannot be hit)