Vanishing buildings

[Mobhack]

Multi-hex buildings vanising if the key hex is destroyed has always been an SP "thing". I put in code long ago to make the other hexes of the multi-hex building register as a building (in the original SSI code, the hexes other than the key were left as clear or whatever terrain IIRC). That was long ago in the MS-DOS days of the game.

But it still comes up from time to time.

As to your weird scenario - looks like you have a corrupt set of terrain tiles?. As zovs said - reinstall, but I would do a windows disk check as well, there may be lost clusters.