I have solved the issue with loosing visibility above 1 mile zoom.
My workflow is this:
1. create/edit map in GPSMapEdit
2. save as *.mp
3. export as *.img
4. install *.img into MapSource with MSTK
5. open MapSource to inspect map
6. uninstall map from MapSource with MSTK
I repeat this process each time I want to change a value or edit a specific map detail so I can see how that change will appear in MapSource/BaseCamp (I use MapSource because it loads faster than BaseCamp, and I am impatient).
I have discovered (at least on my Win8 64-bit PC) that each time I make changes and reload a map into MapSource using the same map ID, the changes are not displayed, and only the original map installed with the specific mapID will be displayed, even after uninstalling any previous versions of the map and deleting all associated files.
If I want to see changes each time, I have to install the map with a new mapID every time.
Have any other users experienced this issue, and if so, how can I force MapSource to clear it's cache?