I have converted some separate 1-25k and 1-50k topo maps of the same areas from JNX to IMG format using Alex's method.

In GMapTool, I changed the draw priority of the 1-25k maps to 31 and the 1-50k maps to 25 with the intention that on zooming-in the map would change from 1-25k to 1-50k at 200m. In my GPS device, each map is visible if selected individually, however if both the 1-50k and 1-25k maps are enabled at the same time, the 1-50k is the only map that displays on zooming-in.

Any ideas on how to resolve this?