What I expected to happen was...:
The void to either appear light or dark, not both

What actually happened was...:
The void, trying to produce both effects, became a strobe light

Steps to Reproduce:
1. Use /effect with night vision potion and make it last a long time
2. look into the void at night (you may need to try from above a certain height, not tested)
3. the void should rapidly become light then dark then light then dark...(strobe light)

edit: although it didn't show up in the search results, https://mojang.atlassian.net/browse/MC-6223 was fixed in 13w10b, already resolved