In 1.7.4 I've seen several rendering issues with slabs.I've only noticed it with Cobblestone and Stone slabs, both with regular and upside down variants.

As seen in the attached images:

• sometimes slab faces are rendered in the wrong position inside the block space (e.g. regular bottom-side slabs render their top face at the top of the block space they occupy
• sometimes the whole slab will flicker up to the upside-down position
• both of these rendering issues randomly affect placed blocks, dropped items, and items in inventories.
• sometimes the black hitbox outline flickers incorrectly as well, even going as far as to highlight a block I'm not even aiming at.

This is a visual glitch only. The flickering happens very quickly and not consistently. Although sometimes the improper render will stick around until a block update, which is how I got the one screenshot where the top face is rendered on the top of the block space.

I haven't been able to reproduce it reliably, and I really can't tell whether this is a Minecraft thing, or a video driver thing or what.

P.S. forgot to mention this is in SSP.