re: Why is it that the Material setting that is applied will not "stick" ?
It may be a BUG.
If you use the Facet Editing tool, you can assign a material for the facet in the Properties dialog. The assigned material was still there when the drawing was reopened.
Another way would be to Explode your Part once so it becomes an ACISSolid, then drag-n-drop to the facet. Of course this will destroy the Part Tree info.
Designer, Deluxe, (Professional, Expert, Basic), Platinum
Windows 10 Pro (1903), 64-bit