Hi Nick - yeah this was a problem with writing non-solids to a .3dm file.

I've made a fix for the next beta, so that if you do an Edit/Separate of a solid into individual surfaces and then save those surfaces into .3dm, when you bring them into Rhino the surface normals will be pointing to the same direction as the outside direction of the original solid.

Thanks for mentioning that this was not working as expected!

- Michael