> The 0x4a/0x4b polygon shouldn't be a problem as long as the upper map is transparent.

If you create a map and don't use --transparent, mkgmap will add the 0x4b polygons.
My idea was that mkgmap could detect if two overlapping parts both contain 0x4b polygons as
this is a hint that one was not properly created with --transparent, but maybe this will not
always produce problems?

Gerd