Isengard map bug

[Chief]

So I'm currently playing a game against Ismaldris on the Isengard map (they have the fortress). I've already destroyed orthanc and taken control of all of the other settlements/building plots. they don't have any units on the map, and I destroyed all of the walls around orthanc for good measure. my units and buildings are the only ones on the map, but for some reason the game won't end, and when I check the player status it says that ismaldris is still playing. the only other thing I could find was that one of the orthanc building plots is still there and it shows up green on the minimap.

[Fíli]

You have to destroy the dam in the fortress.