This occurs on me too after 1.4.2 pretty scary update.
Well, it did happen since 1.3.2 after I installed a mod.
I removed .minecraft in roaming folder in user folder before
I installed 1.4.2.
I can ignore if I try but still bugging me since its visible on every single mobs...
When I hit a mob the side of it's head goes white completely. It is quite odd.
I have only noticed this in the 1.4 snapshots/pre-release.
Well, it did happen since 1.3.2 after I installed a mod.
I removed .minecraft in roaming folder in user folder before
I installed 1.4.2.
I can ignore if I try but still bugging me since its visible on every single mobs...
windows7 64bit/ radeon6870/ amd phenom II