When you deselect the automatic update of associative spaces, and divide an associative space with a new boundary object the space will not be divided immediately. However, if you then activate the automatic update of associative spaces, the space is not divided either.
Boundary objects added while the automatic space update is turned off will not be used to update spaces later when the setting is turned on again. Only objects added or modified while the automatic update is turned on will be used to update the spaces. If you encounter the situation above, delete the wall and re-insert it with the automatic update turned on.