Noticed in my current game (my first with G&K), and then confirmed it in a settler/quick/duel/Napoleon.
If you build a land unit in a city, that already has one garrisoned, the city will get +2 more to culture (from policies). If then you move the unit out of the city, that extra +2 disappears, BUT, if you disband that unit while it's still in the city - the +2 stays. And, it seems to be infinitely stackable.
(The happiness bonus from that same policy doesn't appear to stack that way.)
If you build a land unit in a city, that already has one garrisoned, the city will get +2 more to culture (from policies). If then you move the unit out of the city, that extra +2 disappears, BUT, if you disband that unit while it's still in the city - the +2 stays. And, it seems to be infinitely stackable.
(The happiness bonus from that same policy doesn't appear to stack that way.)
