What does this stronghold actually do? It states that if a province is destroyed, then that provinces owner will not refill provinces during his next action phase? What does that mean? Haven't the provinces already been filled automatically during the dynasty phase or some other phase when a card leaves the province and another card is placed face down from the dynasty deck in it's place. The only thing this stronghold seems to prevent is the Border Keep's province refilling action since it occurs during the action phase?
Hidden Moon Dojo
A topic from AEG's L5R CCG Rules forum, copied for Oracle of the Void from a copy of the forum saved in October 2015, so pages it didn't save are missing. Players' names are left out; the rules officials are named. Rulings are as they stood on these dates; later rulings, the rulebooks and the Rules Archive may differ.
What does this stronghold actually do? [...] The only thing this stronghold seems to prevent is the Border Keep's province refilling action [...]
You have perfectly understood what this Stronghold's action's last effect does and does not do, from the rules' point of view.
For more information about Hidden Moon Dojo, see also: "Hidden Moon Dojo and discarding effects" and "Hidden Moon Dojo versus Never stand alone".