Why did I become unhappy?

Hi all,

I'm playing a game as Rome, and I've done a good job getting 4 cities up and getting the NC quickly, but I'm struggling with happiness right now. I have the full tradition tree completed. I had +1 happiness, and 2 cities set to grow the next turn. One was my capitol, which grew from 11 to 12. Since I have the monarchy policy (+1gold & gold and -1 unhappiness per 2 citizens in capitol), I was expecting to be at 0 happiness (-2 happy for pop growth, then -1 unhappy) after the growth, but I ended at up -1. There weren't any other modifiers (losing CS influence or luxes) that I could tell. Any idea why this happened? Maybe I just don't understand the happiness metric as well as I should.

The monarchy policy rounds up while counting pop.

For example;
3 pop=+2 happiness
4 pop=+2 happiness
5 pop=+3 happiness etc.

Pick up Aristocracy soon and you can steal that 1 happiness right back.

Monarchy's kinda weird. It's every other pop, starting at one. You get a happiness point back on every odd number.

Not explained properly in the description, I know.

Thanks, that is weird. There seem to be all sorts of these little nuances in the game that aren't adequately explained in the tooltips or the Civilopedia. At least I'm still getting the bonus, just not at the pop size I was expecting. I thought maybe it capped at 10 or something, and I didn't want to have to slow growth on the capitol. The good news is that a colosseum finished the next turn so I didn't stay in the red long.