I know no one seems to have an issue, but if you really want to stick to the only so many beds - it only assigns beds if you tell your sim to sleep in a bed and my other sims are not sleeping in her bed even when it's the only one free, so basically your one sim you can control. To get around this, I have found that if I put two beds in a room (also works if you have each bed in its own room), have my sim "claim" one - if the other beds that are not mine are occupied, I just lock the door (from my sim) until the sim in the other bed gets up - but if my sim is sleeping, I can just lock the door from others being allowed to come in. Annoying just a tad, but it does let you play by the original rules.
Example: Only allowed 5 bed, but I put six on the lot, one each in it's own room, and my sim "claimed" one as soon as I told her to sleep in it, and the other seven sims won't sleep in it at all. So I just locked the room to only allow her in anyway, the bed is the only thing in the room, so it's not keeping anything from anyone else, and then if the other five beds fill up before my sim goes to sleep, I just lock the door so she can't access it. If my sim is sleeping, I lock one of the other rooms until she gets up so that bed is inaccessible. You could just stick to first come first serve though - but your sim will always have a bed though - so... do this if you WANT to follow by the initial rules.
