Slabs, Stairs and Walls appearing darker than full blocks

Summary:
Slabs appear 1-2 light levels lower than surrounding full blocks, stairs etc.

Steps to Reproduce (Slab):

1. Place a full block and upper slab of any type side by side
2. Note that the slab appears darker than the full block
3. Place a torch on the slab
4. Note that the slab brightens to match the full block

Steps to Reproduce (Stair):

1. Place 3 full block towers 1 block apart (smooth sandstone works best)
2. Place stairs in between to make a square (like many window designs - example below)
3. Note that the stairs appears darker than the full block
   Note: Smooth sandstone is apparent at all times of day however my testing showed that all stair types are affected but most only show at night. Example below.

What I expected to happen was...:
Slabs, stairs and full blocks should react to ambient lighting in the same way.

What actually happened was...:
Slabs, stairs and full blocks each react differently to lighting causing them not to match.