Promotion buttons

[need my speed]

Has anyone ever noticed the borders around some of the promotion buttons are different than others? Compare Medic III to Medic II, for example; Medic II is normal, but Medic III looks different.

 

[Dragonxander PR]

Are you using a great general? If yes the difference is that the promotions with the different border are those that depend specifically on attaching the great general to a unit or unit stack.