It's an odd thing, but community lots in build mode can go live for a split second while saving.
On slower computers, the live mode is a bit more prominent. When I used to save huge lots after building for a solid hour or so, the lot would go "live" for roughly 20-30 seconds, which is crazy. All I saw was the water surface of the ocean that was moving - and it had me thinking for so long until reading your post!
"What do you have to be nervous about? You're someone on the internet." -A.M.R.
20-30 seconds?! Wow. I have only experienced as I said a fraction of a second, but even that has been long enough to create a hairdresser on one lot and a bartender on another and many running frozen fountains. Thanks for that information on slower computers.
"I dream of a better tomorrow, where chickens can cross the road and not be questioned about their motives." - Unknown