Hidden lines disappears after "save as dwg"

Strange problem...
In drawing one part has hidden lines shown.
But these lines are removed in dwg export.


Hidden lines in other parts ore shown and export OK, just one partis missing hidden lines.

What happened?

Left SW, right ACad:
http://img12.imageshack.us/img...23/clipboard01kwy.jpg

SolidworksDrawings And Detailing