When on the edge of a chunk border, you would expect the chunks behind you to still be visible when in the first-person view.

If you get a certain angle right on the edge of the chunk, the chunks behind you will not be visible. This only happens in a 1x2 tunnel. Noticed when strip mining. 

Steps to Reproduce:
Create a 1x2 tunnel by a chunk border, making sure a chunk corner isn't visible.

When the player's rotation is greater than 45 degrees away from the chunk, the chunk behind will unload