When you place a moon too close to the main planet (within the white zone of course) it happens that it is not colonizable by any orbital units. Fabbers nor Astreuses can go to moon's orbit, instead they circle the main planet once and then come back to main planet's orbit. This has happend to me for many times now.
If you remove the word "too" from the title, you get a statement which is depressingly accurate from a social point of view.
