Recently I stumbled upon a problem that left me scratching my head for a while.  Search in Mapsource wasn't being enabled while it worked fine for the gmapsupp.img in GPS.  The _mdr file was several MBs size, so indexing was obviously taking place.  

    After tweaking the build/deploy script, I found that an extra dot in the overview file names was the cause.  The extra dot is due to my particular naming convetion following this pattern: <family name><MM>.<DD>.img  MM and DD are the month and day of build.

    Of course this was simple to fix.  I just changed my build script.  But I think an error or warning could be thrown by mkgmap or at least a notice in mkgmap options help page so others can avoid this pitfall.

all the best and great work,

Paulo Carvalho