If I check the "set materials" option when saving a part or assembly to .3mf format the resulting file isn't valid. When loading the .3mf file generated by SolidWorks via the lib3mf library I get a warning "Encountered warning #32958 : A components object must not have an object-level PID." and the material information is dropped. I think this is because the material identifier is written by SolidWorks against the components object rather than the mesh object in the .3mf file:

<object id="1" type="model" name="Part2" pid="2" pindex="0"><components><component objectid="3"/></components></object>

Does anyone else see this? Am just evaluating the product at the moment so don't have the ability to submit this as a bug but thought I'd post it here at least