Only colonies copy the Capitols setting when being set up.ORIGINAL: Leslac
The event is probably coded to take a certain percentage of your stockpiled money, modified by the roll involved. It doesn't check how long the city has been under your control or whether it's regular or unincorporated.
Now as to WHY it happens, is probably linked to your very low workers wage and probably low worker happiness. I believe newly conquered cities copy your most recent city changes, so you can actually influence what standards are introduced in your cities - worker wages and emergency food f.ex. But it's still somewhat unclear to me.
It could also have something to do with what main stat you're playing with. I tend to get one type of civil unrest event under democracy and others under autocracy.
I'd post this elsewhere, suggestions or the technical forum... The game still needs a lot of tweaking to iron out bugs and inconsistencies.
Conquered cities simply start with the inverse of the Happiness and Loyalty they had to the previous owner. So not having a Riotous relation with them is pretty impossible.
In the Zone orders are set to 0 Salary for Workers, 0 recruitment quote, Unincorproated. I can not remember E-Food, but I think it is turned on.