Not sure if this is a bug or a feature...

[new_civilian]

The random spawning of aliens on (any) terrain leads sometimes to extreme numbers of units in one building. Had a small farm building in my last mission (10x10) and it contained no less than 6(!) sectoids, and a 7th one was running out of it/at the door of it before i leveled the whole thing with rockets.

I like the randomness, but I do not know if this is actually how it is supposed to be...

It would also explain the high number of civilians in one location that some Piratez-Mod users reported.

[Arthanor]

I thought the spawning code was intended to produce groups of aliens. Like if there's one alien in a building, there's usually more that you haven't found yet. Is it really totally random?

Personally, I prefer encountering groups of aliens. It makes more sense that they would stick together to engage XCom rather than spread to be taken out one by one. (And it makes explosives more interesting )