Every once in a while I will go to create an army in one of my cities. I select the unit and press x to create army, however the option to create army is replaced with upgrade unit. I have the option of picking a new promotion for one of my single veteran NEWLY created units, never been in combat units. I have no idea why or how this happens, I can't figure out if it's tech or a great person that makes the city do this. Please help, this has to have happen to someone else. Ex: select build tank>rush tank>next turn press x upgrade unit>infiltration or blitz. Only units built in that city get this option.