I just loaded the UK 50k v4 maps on my 62s and Oregon 600, disabled all other maps and the results are identical on both units: when zooming out I get the European Basemap at zoomlevel 30Km, all levels below show the rastermap. The map contains several layers of rastermaps showing more detail when zooming in.
I also checked it with v3 and I am getting the same result. I like v3 better however because it's jpg-compression is lower, v4 looks really ugly when zooming in.

Did you disable all other maps in your GPS (internal and SD)?