This is a constant problem I have over all versions of Minecraft, modded or not, that I have. When breaking a block, those textures that show cracks in the block are z-fighting with the block's texture. This happens when I'm nearly looking straight up. The 2013-02-14_16.53.22.png screenshot is attached to better show this.

The block breaking texture completely disappears when I'm looking straight up. In the 2013-02-14_16.53.11.png screenshot, the block is nearly broken, however the block breaking texture is missing.