Siege of Stonehold: able to go off the map

In Siege of Stonehold, I have noticed that decoys can go out of the maps at the places where the enemies appear. The enemies follow these decoys off the map and disappear, which causes me to run out of time. Is there any explanation for this?

This should be fixed now. Technically you could still win. You just have to run after them, be faster and catch up to them.

Anyway, there are now (invisible) walls around the map which should stop your decoys to wander off.