I left a citadel on one border of my civ unmanned because I needed every unit I could spare to fend off the Japanese who were attacking from the opposite direction. While I was focused on the battle with Japan, a barbarian warrior walked up and stomped on it. The citadel is still there. It's just ugly and smoking. Workers can't seem to repair it and I can't remove it. I don't know if it still has any defensive effect or not. Is this new or have I just been lucky thus far?