#322085
Yes, if you look in the Scene Manager window, there is a Materials tab. The materials contained there are saved in the Rhino file. When you drag an MXM file from the Database Manager window into the scene (or import an MXM any other way), it creates a plugin material which can be found in the Scene Manager > Materials tab. To edit a material contained in the Rhino document, double-click its thumbnail in the Scene Manager > Materials tab - the plugin's material editor will be shown.

So, is this a known issue?