Shadow calculation

Hello all ,
I have built on my map, shadow were calculated normal, except for the last 2 cps - provide many of these blocks are shown in black - now I wonder how can that be? here are a few pictures of the FIRST shadow calculation:
now the second shadow calculation - the normal blocks shown I have NOT built later, but the whole map calculated once, and this is the result:
have any idea if this is normal?
I have built on my map, shadow were calculated normal, except for the last 2 cps - provide many of these blocks are shown in black - now I wonder how can that be? here are a few pictures of the FIRST shadow calculation:
now the second shadow calculation - the normal blocks shown I have NOT built later, but the whole map calculated once, and this is the result:
have any idea if this is normal?