If I read your post correctly, I think in Navigator, on the PC, after switching to version 8 in the top bar, you need to unselect all maps, and reselect the maps you wish to use.
If you didn't unselect, then the maps you loaded were version 5 (Still selected from the saved file, and still loaded on your PC). By changing the drop down to version 8, you just changed what is displayed on the screen, and any new maps selected will be version 8, not the old ones that were already selected.
Hope that helps.
(Hope its right)
That is what I did for my GPSMap 60 Csx and it appears to have worked just fine.
2008 BMW R1200RT 7200 miles
2005 BMW R1200GS 13000 miles (Sold)
2002 Yamaha FZ1 (Sold) 11000 miles
2002 BMW K1200LTC 29900 miles (Sold)
2002 Yamaha VSTAR-650 Silverado (Sold) 9100 miles