There is a black blotted part of the screen on the lower-left side of the screen when looking west (most prominent at -46.7/24.9) Here is two screen shots with the black parts in it. This only affects stone. The first screen shot is of the black bar alone. The second is the black bar and debug information screen. [EDIT]Reproduce:
Set priority of Java TM SE Binary process of MineCraft 1.8-pre3 to high.
Go down to this seed: 79650213
Head to -240 X 11 Y 266 Z.
Then rotate mouse until: west X/Y: -46.7, 24.9.
If this is an issue with my graphics please tell me.