Hi Puz, it is possible for it to happen in v3 too - the SAT importer will do this if it has certain kinds of errors when processing the imported trimming boundaries.

So it's likely to be something that's specific to that particular file. If you make something simple in v4 like a box and then export it and import it back again do you get a solid?

Is it possible for you to send the file to me at moi@moi3d.com so I can take a look?

- Michael