Soulsand doesn't get affected by ambient occlusion (Smooth Lighting)

Smooth lighting, at some point after release 1.13, stopped working on soulsand. I only now just noticed it while flying around in 1.18. I went back and found that after 1.13, the issue was there.

 

Below are some comparisons from 1.13, and 1.18 with the smooth lighting option turned on and off.