With the changes to the lighting system, some blocks' faces are black (entirely unlit maybe?) when other blocks are placed on them.
Here are some examples:
{F7972}
{F7974}
{F7976}
{F7978}
{F7980}
[[ http://imgur.com/a/8kXRc | Imgur Album for the Images ]].
I've noticed that this does not happen in some orientations and I'm not sure if it happens to all sides. It also doesn't always happen in a less lit area.
Light emitting blocks seem to be entirely unaffected. Transparent blocks behave similarly to non-transparent and non-light emitting blocks but it's slightly less noticable.
I don't have shadows turned on and the area is very well lit (but lighten mode is not on, it makes the black faces normal).