Ah, Gen Hicks, you caught me. The description says "Laufkontur von eckig auf rund." (Barrel contour changes from angular to round). However, in my mind a double square bridge remains one, no matter if the rear bridge is mutilated or ground off. Also, as far as I know, there are no solid left wall single square bridge actions.

The reason I didn't notice the alteration to the rear bridge is that I have a double square bridge Oberndorf Mauser with a Suhler Einhakmontage and the rear foot is dovetailed into the square bridge without otherwise changing it.