The Blindness fog renderer does not consider that other Blindness instances may be shadowed when the fadeout animation is played. What this means is that when there's a shorter Blindness instance that's shadowing a longer one and the shorter one ends, the fog fadeout animation plays, and the player is temporarily able to see beyond the normal range that the longer Blindness normally allows for. This does not happen if a longer instance is shadowing a shorter one and the shadowed, shorter one ends.

This also happens to the Darkness effect's fog fadeout animation.

I develop a mod that deals the Blindness effect to the player on the client side, and discovered this bug when playing with other mods. I decided to investigate and discovered it happens in the vanilla version of the game, without any mods.

Steps to reproduce

1. Get inflicted with a long lasting Blindness effect instance
2. Get inflicted with a shorter Blindness effect instance that shadows the first one
3. Wait out the shorter Blindness instance