I have created a creeper farm that is between y 108 and y 123.  The on the ground level (y70) the shadow under the farm is correct.  I have create an AFK spot that is way above the farm (y194).

The problem is that the shadow my AFK platform casts is offset about 16 blocks to the north when the world is loaded.  If i climb all the way up to my AFK spot, and then back down, the lighting is correct again...until i next load the world.

The first screen shots shows the shadow on the ground (just dark enough to spawn mobs) and the second screen shots shows me standing in the middle of the shadow looking straight up (notice the Sky light level on the debug text is 7).