This is one of a few bugs I've seen in almost a week of play. I, too, am using a GeForce4 MX 420.
Here are some other problems I have seen; I wonder if they are common to everyone here:
-I have had crashes on wonders videos very rarely, but I'm loathe to turn the videos off as they're so outstanding.
-Unexplored territory is visible where the map wraps around until you move directly over the unexplored territory, at which point it blacks out properly.
-Floodplains and the river next to them are visible through the fog of war.
In addition, I seem to have been given mislabeled discs; the install disc is actually the play disc, and vice-versa.