Toposolid from Cad creates a void in the wrong place

[smartplans]

I have created a DXF topography file using QGIS  which when imported and converted to a Toposolid  creates a void area that should not be there. This did not happen when creating a topo surface from cad import.
The graphic below shows the DXF in its imported form on the left and the converted solid on the right. The hole on the left has been created by Toposolid and interferes with the building placement. Can anyone assist?

[vitorbortoncello]

edit toposolid boundary (double click) and remove the hole

[ridantuo]

I've fixed these so far by making a dummy boundary (rectangle) around the topo lines in the DWG/DXF and giving them an estimated elevation.

EDIT: Luckily I haven't had to work on or close to those boundaries yet.