Sometimes we get some not so nice visitors. They place their army in front of the town and demand a toll and oppress you to pay, or they will attack. If you don’t click their message, they wait up to a year (as a side-note: a wait function would be nice, to not have to leave the window on screen the whole time).
But while the army is waiting patiently, sometimes the siege devices they brought with them start to attack right away. And although the attack hasn’t started yet, they begin to turn down walls and towers solo, as they are almost immortal to ranged attacks. I think, this is a bug, and the siege devices should wait with the rest of the army?