Entering dimensions or disconnecting from servers doesn't show the dirt background

The Bug:

Entering dimensions or disconnecting from servers doesn't show the dirt background.

This issue did not occur in 1.12.

Steps to Reproduce:

1. Join a singleplayer world and construct a nether portal.
2. Enter the nether and as you switch dimensions, look at the screen that you're shown.
3. Take note as to whether or not entering dimensions or disconnecting from servers doesn't show the dirt background.

Observed Behavior:

The dirt background isn't shown.

Expected Behavior:

The screen is just simply darkened.