Undead mobs burn in sunlight even after the Wither darkens the sky

The Wither, as we know, darkens the sky, which is supposed to prevent undead mobs, such as Skeletons and Zombies, from burning in sunlight. But this isn't what I've been seeing.

Steps to Reproduce:

• Spawn the Wither.

• Spawn at least one undead mob. Must be one that can burn in sunlight.

• Observe the results.

Expected Result:

Undead mobs don't burn in sunlight because of the darkened sky.

Actual Result:

Undead mobs burn in sunlight despite the darkened sky.