What determines disband income?

[Xoon]

Sometimes when I disband a unit is a city, I get shields in return. Other times I do not. Ususally when I really need the shields, I don't get them, but when its not a big deal and I'm just downsizing my army, it gives them to me. What determines when this works?

 

[simwiz2]

you cant get bonus shields if you are building a wonder/small wonder/palace. All other times it should give you the shields

 

[costanza]

You will also not get sheilds if your city is set to Wealth. This happens to me a lot later in the game when my city governor decide that I need a billion explorers. After they are built, I just disband them in the same city which has then switched to either wealth or another explorer.