I was playing with Isengard in easy mode vs gondor in dunharrow. I was using the top side of the map. I built 2 expansion sites, at west and the east of my base, in both I built mineshafts to the sides and a tower to the side facing the enemy, then gondor with batering ram destroyed, the tower and the central building and left. The problem was I couldnt rebuild the center building nor use the buildplot where the tower was despite I could see the buildplot like avaliable but unclickable(only where the tower was, the center plot showed nothing) in both expansion sites happend the same, So I have to destroy the other two building to fix the bug. It worked with both expansion sites.
In the same game when I built the furnances in the castle the portrait didn't show the discount, only shows 0% although I had already 3 of them. I didn't check if discount was applying when I bought the improvements on units
The version I was playing was 4.5.4.2