Question about orders and defending

[Starry Vere]

If I set a commander's order to something other than defend, and the territory he is in is attacked, will that then mean that he does not participate in the battle? It seems like that is the case, but I never noticed this until I installed some mods.

Was this a mod change? I thought before (in vanilla) that I could say, order a commander to research or something, and if the territory was attacked he would still participate in the battle.