At war with Armenia, I bribed one of their family members recruited some mercs and took the city of Artaxarta. Two turns later an army arrived to take it back. As I had no missile units, I thought I would sally once and try to lure them to the towers to whittle them down before the main assault.
All was working to plan when one of their spear units running next to the walls had a man run through the wall to the inside of the city!! The rest of of the unit began circling at an inverse corner and more and more of the little buggers started popping through. Thinking this was an odd quirk and there were only a handful of them I didn't worry too much but... the little blighters went to the gates and lo and behold took them!! Much to my dismay the rest off the unit soon came pouring through.
As everyone loves a happy ending, I was of course able to destroy the unit and retake the gates.

This is the first time I have had this happen. Has anyone else experienced this?
Though this is also the first time I have have a city with irregularly shaped wooden walls. Is this a problem with these types of walls or does it happen with the more common square shaped cities as well?