Hrm, I'm suprised at some of the replies to this.
C2L, I know exactly what you are talking about. I've seen this bug in every version of GalCiv2 I've played on multiple computers and it acts just as you describe.
It is not inteneded behavior. It's a bug that under circumstances described above, grants the player full vision of a region of space he/she should not be able to see that will persist until a new game is started.
There were one or two updates a while back that mentioned Fog of War issues.
I recommend sending a bug report to [email protected]. That's the most reliable way of letting the developers know of an issue.
Next time I play and encounter the issue, I'll try to remember to submit a support ticket as well. i haven't done it in the past since I was more interested in other issues.
To sum up, it's not your computer, your hardware or drivers, it's the game failing to re-fill the fog of war under certain circumstances.