Bug: Black dots blinking after expanding

[digitCruncher]

I figure this is a bug that happened in the rare cases where people expand the land...

After getting land expansion, and expanding to the north, I get a black dot appearing every few seconds in the top land. Specifically, one tile turns completely black for a fraction of a second, and then turns back to normal. The game crashes intermittently after the black dot starts appearing, and the lighting calculations for about 3-8 rows below the black dot need to be recalculated.

It might be that the black dot appears after prisoners appear in the prison, so I will confirm if that fixes it.

Anyone else having this issue? I might be able to provide a save if people cannot reproduce it, but it is late.