The fact is, the code means you can only build four per sector, and that's it (same as the AI has to do).
So, by building more than four, you're causing the code to corrupt. Think of it trying to show the starbase, it's image, it's stats, etc, all the while the game is saying "No, no, no, no, shouldn't be there, killing starbase..", while the code confirms it's there.
Think of yourself, believing you can walk through a wall. Your brain is saying "Yeah, sure, I'm walking through the wall" (With certain "illicit substances", that may be a viable option), while there are various laws of physics saying "Ummm, no, I don't think you're doing that".
Result: a broken nose.
Probably wrong but easier to understand. Whatever's happening, you're making the code argue with itself, which is a wonderfully spectacular way of making a computer CTD (from the coding point of view)
