Sprites are completely covered with shadows.

[Barry]

When a shadows goes over a sprite, the whole sprite is covered with a shadow even if the shadow goes over a part of a sprite, but it can
also happen that the shadow goes over a sprite, but does not do anything to the sprite. I think it can include lights, not just shadows.
Here is a fan that reflects a shadow to the ground:
http://i46.tinypic.com/280kxv7.jpg
Here, an imp turned into gibs is under the fan:
http://i50.tinypic.com/2gvt2s5.jpg
Here, the fan's shadow goes over a part (middle) of the gibbed imp, and the shadow covers the whole sprite with a shadow:
http://i50.tinypic.com/2a9r1on.png
Here, the shadow goes over a part (right side) of the sprite, but nothing happens to it, it just stays as bright as it is under the light:
http://i49.tinypic.com/ayau60.jpg
This is probably not a bug, because it is a sort of situation where you have to change the sprites, so that it would react in a other way when
there is a type of light or shadow going over it. This might have in some sort of way a connection to Enjay's thread he made not too long
ago: "r634 Sprites too bright under certain conditions"

[Graf Zahl]

Not a bug. Doom can't do better.