I thought this mod was suppose to work with the RetaingWallsNeverDie mod?

Using the Extended walls I made a rectangle area that was 5 above the games base level. The walls were level with the ground. I then tried to dig out to -5 (10 levels difference) using the sandbox mode. Nearly all the walls immediately collapsed. Tried with the 1.2.1 and 1.2.2 versions.