When viewing blocks from a certain angle if they are touching the edge of the screen they will become see through as if they are not rendered at all. If you ask me and my uninformed opinion it is as if the code that decides whether a block is seen by the player or not and therefore is rendered is not functioning properly. I have attached screenshots displaying the issue.

This happened as far as I can tell no matter what I did; switching versions of java (sun 6, 7, openjdk) fast or fancy graphics, optifine or not.

How to reproduce: In an environment similar to mine stand next to a contiguous wall of blocks and look at a block on the edge of your screen at a certain angle. It might seem like it is only flickering at first but if you focus you can find an angle where it just disappears (at least for me).