The player marker / icon on maps created in the nether is supposed to rotate all the time. However, other markers and icons are rotated randomly as well when added / updated.
It might be intended for the green item frame marker, but is is very likely not intended for markers which normally cannot be rotated, such as banner markers.
- Create a map in the nether
- Right click a banner
→ The banner marker is rotated
(You might have to add multiple banner markers in case they randomly got the correct rotation)