Hi, thanks for the report! This is not really a bug per se. The area indicates the area of space under control by the star. I don't want it to be infinitely large (or bounded by the map size) since this would fill areas between galaxy arms or regions between contintents. So this is a very non-trivial thing to "fix" I'm afraid.
The easiest fix may be to squish stars closer together, and I think this works quite well with non-insane galaxy sizes, but maybe I can tune it for insane galaxy sizes.