Normally, when one of your units wins a combat that gives it enough experience points to be promoted, the promotion can't happen until the next turn, right? An annoying thing, when said unit is damaged and could use the healing + benefits of promotion during the AI's turn, when it will be facing a counterattack. Well... I just noticed that if a unit goes into combat with a promotion unused (for example, a Privateer fresh out of the Drydock but at 4/2 XP - meaning it started with 4 XP and you haven't promoted it yet) and then fights, winning enough XP to hit the next level (again using my example, putting the Privateer at 6/2 or 5/2), you can use all promotions immediately, even the one you just earned. No waiting until the next turn. Bug or feature? In any event, it has limited applicability, since you'll usually want to go into combat with all promos used.