i am sorry to inform that the buildings are still burning werd sins one building i got have 99999/1000, so wery werd that it still burn, some units also have a red health bar means low health even do they have 99999 health......
Did you check with a new game where buildings weren't already on low HP? Can they take any further damage or do they get destroyed in an instance and the 99999/1000 is just cosmetics?