Hi Stefan,

re:
> Regarding my statement about the bug - I still think there is something wrong. When I
> selected the part to be exported, it was visible. That's how I saw in the preview that it
> was broken. But the exported file was still "empty".

I'm not able to repeat that bug over here... Here's what I did - I opened up your "broken_after_isect3.3dm" file that you attached above, then clicked Edit > Hide to show objects since they are all hidden to start with, then selected one of the large pieces and did File > Export to a test 3DM file, and then when I opened that file it had the object in it as expected.

Did it happen with a previous saved version of this file? If so can you please send that one to me so I can try to reproduce the bug over here?

I won't likely be able to fix the bug unless I can reproduce it.

- Michael