I'm playing as the Romans and currently in a pretty big war with the Macedonians. Anyways, they have this one stack that has a couple of Scorpions in it, and everytime when they siege a city that I took from them they just stand around until the battle timer runs out. I even take my Cretan Archers out of the city and shoot at them, and they still don't bother to move. I'm pretty sure they do it because they consider scorpion a siege weapon and they're waiting till it breaks the towers or the walls, but since the scorpion can't attack those they just keep waiting forever.
I'm playing RTR PE 1.6 with BI exe so I don't know if it's just the problem with BI or does this happen all the time.