The lighting engine was supposedly fixed in 1.5, but while building something in creative on my test world I came across another lighting glitch. I had thought that the lighting bug would be gone but it is not.

Steps to Reproduce:
(In case I don't explain this very good, there are screenshots)
1. Make a pillar that is 4 high like this:

xx
x0

x = block
0 = air
(I don't think height matters it's just so you can see it)
2. Make a square of half slabs on the front of the top block:

xx
xhh
0hh

h = half slab
0 = air
3. Add another half slab on top of the top left (if you are looking at it from above) halfslab.
4. The lighting glitch will occur underneath that set of half slabs.