The ultimate cause of the problem is use of background color for fill, which is not supported for entities other than wipeout which only supports polygons in ACAD. When you are in DWG workmode, you wouldn't be able to use background color, hence eliminate the ambiguity of defining color 255. The downside is that you won't be able to create wipeouts. You may create a hatch with a color close to viewport background color as a workaround.
For element sorting, besides the obvious bug we shall fix in the future, the best way is still to use Element Priority, as that serves the very purpose to control the order in which elements are displayed.