Single player survival worlds, with cheats enabled, tested on two computers (identical OS and JAVA)

After a visit to the nether (NOT the end) the world spawn, the point the compass points to, changes to the following coordinates: X=8 Z=8 instead of staying in place.
I noticed this first in a world where I had used the /setworldspawn command. Easy to reproduce in a new world (tested it in 5 different worlds. without using the command, on two PC's)

Steps to Reproduce:
1. Create a random world (flat or normal survival)
2. Mark spawn with a compass
3. Build a nether portal and travel to the nether
4. Travel back to the overworld
5. Follow the compass to spawn,
for me this leads to a new location at X=8 Z=8, every time.

Tested in Survival and Creative.

Attached are three screenshots taken from a test world.
1- is the spawn location before going to the Nether for the first time.
2- is the same location, after visiting the nether, with the compass clearly pointing a different direction.
3- is the new spawn location.

EDIT 1:
After exiting the world, and loading it again, spawn resets to its old value (the one set by the command or original spawn in the test worlds). Going to the Nether changes it to X=8 Z=8 again)