Chunks don't always unload

[PetteriM1]

Expected Behavior

Chunks unload after a while when there's no players online

Actual Behavior

Often a couple of chunks stay loaded

Steps to Reproduce

1. Join the server and fly around to generate some chunks.
2. Disconnect.
3. Use status command via console to monitor the amount of loaded chunks.

Notice that by default a few chunks at the spawn area stay always loaded. Test it further away from spawn.
This issue seems to particularly affect newly generated chunks and can cause significant memory usage on bigger servers.