The swordsman triggers the trap most of the time before we get to him. This results in potential ally being killed, or, if the trap is falling door, roaming free. It would be less frustrating if he doesn't move before the door to his cell is opened.

There are other "shit happens" moments in ADOM (for example cute puppy killed by a random monster) where there is nothing player could have done to prevent them, and this is fine. However, in this instance the probability is way too high.