@x-trail

In most maps, the background type is 0x4b for a non NT map and 0x10d01 for a NT map.

I can produce the above result in Mapsource and Basecamp by adding to the map's TYP file the polygon 0x4b (Map Background or Data Bounds) without any Draw Order.
When I transfer this map to my 3490, 205w, GarminMobilePc and Streetpilot Android the result is that this polygon is shown transparent (????)
To avoid some issues, it is advisable to add that polygon ( 0x4b for non NT map or 0x10d01 for a NT map) to the draworder list ( in the lower level i.e. 1).