Hi Martin, so that one is simple enough that I'd expect for it to work, but you're running into some kind of a bug. I may have a shot at fixing this one since it doesn't involve extension problems.

Doing a shell seems to be ok, so another workaround for the moment is to do a shell instead and then extrude up the bottom face of the shell and boolean union that extrusion with the shelled part.

Quick note - whenever you want to push the "Done" button you can use a shortcut of just right-clicking inside of the viewport instead of moving your mouse over to the actual button.

- Michael