Put the summary of the bug you're having here:

• Cracks in wood (tree trunks) while breaking the block of wood have the appearance of z-fighting, or cracks don't appear at all.

What I expected to happen was...:

• Start hitting a block of wood, get nice clean 'cracks' until wood block is harvested.

What actually happened was...:

• Start hitting a block of wood, cracks flicker while hitting the block of wood. Depending on where I hit the block (on a corner, from the top, at an angle, etc.), sometimes the cracks are not visible at all but the wood particles still fly off the block of wood until I harvest the block.

Steps to Reproduce:

• Find a tree.
• Hit the trunk until cracks start to appear. Observe cracks, then stop hitting it before harvesting the block.
• Move somewhere else and hit the same block while observing the cracks.

Observations:
I noticed the problem started at version 14w06b. I cannot reproduce this problem when I play the same world on 14w05b. The problem looks similar to z-fighting (the look you get when two textures are one-on-top-of-the-other), except the flickering is identical on all visible sides of the block. The problem is more apparent if Minecraft is played with 'Advanced OpenGL' turned on, but is still visible whether it is 'on' or 'off'. Hitting other blocks (stone, wood planks, etc.) have normal cracks with no z-fighting.