I believe there is a bug relating to planet quality and the number of tiles available on a planet. In story form since I don't know what's significant:
Once upon a time, playing the current 1.2 version, I conquered an enemy planet via invasion. My civilization was aligned neutral, and the planet was a class 12 with no soil enhancement/terraforming performed on it. After conquering the planet, it increased to a class 16 but still has only 12 total tiles available for building. This seems to happen every time I conquer a planet, either by invasion or influence. Seems like the neutral ability to auto terraform tiles is broken during takeovers?
I have save games that exhibit the problem, let me know if anyone from stardock wants them.