Certain items will flicker between being bright and dark as you move around them. It doesn’t matter what the actual light level is. This bug does not occur in beta 1.7.3 or older, so it is probably a multi-texturing problem.
Affected items: signs, chests, double chests, boats, minecarts, player’s arm, books on enchantment tables
Graphics - Mobile Intel 4 Series Express Chipset
Most other people with this problem have Intel graphics
It must be something from your video card.
I've experienced the same thing with an Intel card on another PC, but, it's certainly a video card problem.