True spawn and spawn chunks move after returning from the nether.

I expected items within the spawn chunks to despawn after 5 minutes (I was waiting in the nether).

After 5 minutes I returned to the over world. None of the items had despawned. I tried multiple times and eventually rechecked the true spawn with a compass. It had moved over one hundred blocks away.

Death seems to reset the true sapwn to normal, but it moves again after being in the nether.

Steps to Reproduce:
1. Enter the nether.
2. Exit the nether.
3. True spawn moved.