Forts Recapturing Provinces?

[Warhammer: 3025]

I've noticed that sometimes, when capturing territories around an enemy fort, the provinces will simply "uncapture" themselves. Can I make my own forts do this? Is it a feature of some DLC I don't have?

 

[Vincentst]

Normally your own forts will do these automatically, if they are maintained. It symbolizes the garrison of the fort which will recapture the area.

 

[Sfan]

Any province adjacent to a fort will flip back to the fort if it is besieged by an enemy which leaves the area, unless there is a force on the province or on the fort (it can very well be a batter regiment of 0 men, what matters is that there is something). It only works in your land, not on forts you occupy, they do not automatically get control of nearby provinces. That also works with rebels, your forts will recapture adjacent provinces after rebels move out. On top of that, provinces adjacent to a fort won't get any additional separatism when occupied by nationalist rebels.