As shown above, the armor stand has an item on its head rendering as a block that has the same texture as a purpur block. It is darker than the real purpur block. The zombie is also an example. The top might be brighter.
On the right is a falling block, which has proper lighting.
Smooth lighting does not have the same problem. The bug is still present with every brightness setting.

This also affects block_displays and item_displays in 1.19.4