This isn't a bug, so this should not be reported here.
I believe this is intended behavior.
Add some more detail please?
This could just be void fog, which was intentionally added to the game around Beta 1.8. The Minecraft Wiki says that Void Fog affects all layers from Y=28 downward, so this is merely an annoyance, not a bug.
Give some more information, please! What potion effects, and what other circumstances?