No terrain on Minimap (with pictures)

[10shi]

I have the complete sid meiers civ IV version and i'm playing vanilla bts. Sometimes when i scroll around the map or zoom in, all terrain on my minimap will vanish. This happens in about 60% of the games i've played. is there a fix or something?

**edit: I'm on version 1.7.4 for civ IV and 3.1.9 on bts