And another great feature:
There's a quest to upgrade 3 residences ... so to get it faster you build 1 new residence (within seconds), upgrade it (within seconds), delete it, build the next one etc. until the quest is done.
So far, so ok. The quest is done in less than 2 minutes.
If you look now at your total/available population, you'll notice that population has been added due building 3 new residences, but (maybe for not waiting until upgrade terminates before delete the new residence, because starting upgrade already was valid for the quest ...), the added population never has been removed and is available for what ever you want ...
Once reloaded the game/site, population is set (back) to correct number.
Best regards,
Extranjero