Greetings all.
Based on your suggestions, I made a few tests. Here are some details:
1 / the original .dwg was created with sketchup, as I do not own Architect.
2/ I opened a new file, then imported the dwg, then started drawing.
Apparently, this was my mistake. As I am a newbie, I didn't think to check nor could I imagine that this single action would trash my dash styles!
3/ after all this discussion, I did try what Ray suggested above - namely, I imported the file, then copied everything to yet another new file, which of course worked fine.
Therefore, I made the following conclusions:
a) the VW .dwg import module has some kind of bug if it always creates this problem (as evidenced by both my experience and the comment of Master Pickup, above;
b) maybe we should suggest to Nemetschek to add another routine which automatically copies everything into another document (?) or whatever, which would then assure that no dash styles are damaged?
c) (sadly) i have no idea (yet) what a Workgroup Reference is but I imagine it is something like an XREF? In any event, it sounds like a good idea...
Finally, if anyone is interested in testing the "broken" .dwg file, I am happy to send it. Just send me a pm and I will email it to you. Its very small.
I've also decided to upgrade to Architect now and will test what happens with the same file if I go direct from SU to VW...
best to all from Berlin,
Jason
PS to Ray: I've sent the buggy .vwx directly to the Tech people at Nemetschek. It seems that it has been submitted as a bug ... if I hear anything else I will post here.