The problem I have is described below if someone want's to know about the "why".
My toolbox components loose the Material specification (it changes to "material not specified" for currently selected configuration) everytime I drag and drop them into an assembly. I know its a bug. It's been confirmed and it's most annoying. Plus it's been around for a long time and SW isn't helping. With SW 2013 I could open the component and simply select "reload component" and it would update the material specification. In SW 2016 it got worse. A simple reload won't work anymore. Now I have to additionally open & close "configure Material" dialog window before reloading the part. ("that's upgrading spelt in SW's world")