What I expected to happen was...:
Coordinates while teleporting from Nether to The End must be like while teleporting from Overworld.
What actually happened was...:
Coordinates when teleported is equal coordinates of portal in Nether
Steps to Reproduce:
1. Use any world
2. Tp to Nether
3. Go to any coordinates (like x:1000, z:1000)
4. use /setblock ~ ~ ~ minecraft:ender_portal
5. When you in The End press F3
6. Your cordinates don't changed
If use 2nd and next portal in any world you teleporting to x:1000 z:1000, but don't for main island.