I prepared a response, but probably closed Firefox tab before sending

So once again: this map really has 2 layers. One is routable, second non-routable. Second layer probably is for additional addres search in some cities (just my guess).

Corrected version 5.2 should display single map in menu too. Probably your nuvi didn't notice, that you rewrited map. You can use option "Refres header date" from gmaptool "Write" tab to force rescan of modyfied gmapsupp.img (this is advanced option, you should turn on advanced options in "Options" tab).