This is not a problem with Minecraft itself, but with your Graphics card. This happened to me on every game when my graphics card started going bad. I would suggest checking other 3D games for this bug and monitor this, if it gets worse you will need to replace your graphics card
I do believe there is no '0' frame (At least it was like that before)
This isn't just the end, its whenever the boss health bar is rendered.
@zombiehunter, No, this is the right place
@Jesse: I was off by one version, I tested and during alpha lighting errors like this would occur under trees, but not overhangs, But Beta 1.1 fixed the trees but brought in this current bug
This has been happening since Beta 1.0
@Kanghun But he was placing it on a top-half slap, the slab was on the top half of a block, meaning that he should be able to place it
Mob spawning isn't seed based, it is random (Correct me if I am wrong)