Selecting "Undefined" lines
When saving an xml-file the unused lines (walls) are saved as "Undefined", which is good. But most of the lines are saved as transitions and not as walls. When reopening the xml-file the unused lines are displayed and can be selected, but they can not be added to a room or as a door, so you have to draw them again.
It's the same, if I draw the geometry by hand and do not use an dxf-file.