Loading into a world speeds up background panorama

Steps to reproduce the issue:

1. Create a new world (Superflat in this example).

2. Exit to the main menu and reload the world.

3. Observe the background panorama while the world loads (visibly sped up).

Expected result:
In release 1.21.11, the background panorama does not speed up during world loading.

Note the versions that are switched between on the upper-left part of the footage.

Actual result:

While loading the world, the background panorama speeds up for the duration of the loading screen.