Lighting with slime blocks is incorrect, pictures below show.

Steps to reproduce:
1. Create a 5x5 area with Mossy Stone Brick Monster Egg.
2. Make the inner area 2 deep.
3. On the 2nd layer place slime blocks.
4. Switch graphics to fast, and smooth lighting to maximum.
5. Observe incorrect darkness on blocks.

To further this place a glowstone block in the middle, which is supposed to light surrounding blocks, and notice how it actually makes the slime blocks darker.