Hello dellus,
I just "produced a new .dxf and tryed to get the error, but it didn´t come.
To the history of files: I took a .jpg from internet and, in the first time, I tryed to convert for use in WinMegacad 3D V13. It took some time to get it, cause there where many wrong ways. Reason may be, that inkscape and libre are new softwares and Megacad isn´t. So it takes not all dxf´s. Sometimes I saw, that my Megacad is to old and/or my ways for conversion are to complecated. I discovered, that inkscape can export directly to dxf after vectorizing. In my memory the describt file is one of them they came from Megacad. May be they don´t match.
My solution to now was to use hor. and vert. lines with a defined high length. But your guess may be right, so I can press this to the trashcan.
Thank you