I have used the split wall command and the wall is indeed in two parts but I cannot work out how to separate them. If I select the first part and go to Modify Walls and change the end point, the start point of the second part moves with it. Conversely if I change the start point of the second part, the end point of the first changes. Basically, the two parts are not separate.

Of course I have also tried having one section selected and dragging the end of the section away from the other.

I tried having one section selected and reversing wall direction, but that didn't seem to make a difference.

I tried selecting both and and seeing if you needed to do split wall again, but the command isn't there anymore.

What am I missing?