Blocks with multiple textures such as half slabs, pistons and stairs, will randomly glitch, flickering back and forth between different states.

This bug occurs when blocks are held, when they are shown in menus or on the hotbar, and when they are placed in the world.

Half slabs will flicker between half and full blocks.

Pistons will flicker rapidly between extended and retracted appearance, (just the piston block itself, the arm seems unaffected). (See pics)

Not sure how it's related, but block updates within approximately a 5 block radius will cause placed pistons to randomly switch texture between retracted and extended appearance.

As a side note, I performed single-word searches for "glitch" "texture" "flicker" and "piston" and none of these words returned a related hit on Mojira. I would be shocked if this issue has not been reported already, but if this bug has already been reported, then the Mojira search engine needs an update.