Bro, despite I change my orientation setting to "Track Up", the facing-direction is still wrong when my car stops. The map will just turn clockwise and my direction isn't aligned with the straight road. Could it be the electronic compass?
I did try loading another map with the name "gmapprom.img", and the whole unit was hanged!

It cost me a few hours to fix it.

However, to my surprise, I found that using a totally different name such as "topography.img" or other simple english name will just do the job.
The device reads the map seamlessly, and I'm able to disable the relevant map when I don't need it. Hence, I compile a standalone topography map instead of merging it - and it works fine together with the normal MFM map

Heew... what a day.