Not sure this is a bug but i think this might be a balancing issue. When you siege a castle of an ai player before all enemies are killed itll say victory, but there will be several enemy units left so hart to get workers in to loot but at same time the clock will start counting down from 3 min. for example yesterday i was siege a orc castle after a brutal fight it was declared i was victor however a good portion of enemy archers were still on the wall and the spike traps were still there which made it impossible for my workers to get to looting anything. Now i know returning to world map loots for half but isnt that kinda the point to get to loot all that castle's stuff. My suggestion is on the castle siege part to take the time off at lest
for the ai player.