Unique quirk with Nurgle

As some of you probably know the ai massively overvalues military barracks when you sell it land. Playing Kugath I wanted to sell Tretch some land so I could raze cathay in peace so I built 2 barracks hoping to sell it for a lot of relation. To my shock the value of the settlement went down to -1704 because of the military barracks. As far as I know this only happens with Nurgle as a faction.