Short description of error
If 2 surfaces are above each other, they won'r render correctly after import.
It's due to a problem in Blender's code to draw curves, but an option to import as mesh to avoid this problem should be given then.
Converting after import to mesh is not an option as it will create a mesh with the artefacts seen in the viewport and will triangulate everything, creating lines that don't exist.
Exact steps for others to reproduce the error
Import this DXF:
This is how it should like:
This it what is blender after import: