Income of Cities won't increase with population / development?!

I have been playing my current game of MTWII with objective of creating a rich empire, which includes cities that produce large incomes. However, I am having trouble with couple of cities just not increasing there income. At the end of my post I attached the income that have decreased/stuck after 14 turns. :shrug:

I have increased population in those cities, build economic buildings (grain/markets, roads, ports, farms, etc) but the income isn't budging. Take Leon for example, in 14 turns it get new stone wall (city level uped), population up by 65% / 4,000, yet the income decreased by almost $100. Shouldn't it be going up?

Only thing that went down a bit was public order to 120. So I did test and added a Governor to another city (Cordoba) even with increased public order and population the income is down.

This is making no sense to me. Seems like I am spending tons of $$$ building these cities up but am not getting an income boost out of it!!! :wall:

http://oi41.tinypic.com/2hyicjp.jpg