I noticed this in my debug.err when the map music cut out on me after settling my first village:

DebugMessage:  Could not find music file name for layer with index:0 in music group: MapTheme7_Arrangement2

So I looked at the CoreLayeredMusic file:

So that made me look in the FE/LayeredMusic directory, and, sure enough, there's no "MapTheme9". There is a "MapTheme9a"

Entries where I see a seemingly non-existent file referenced:

"MapTheme5_Arrangement2", "MapTheme5_Arrangement3", "MapTheme5_Arrangement4" (references non-existent MapTheme9)

"MapTheme6_Arrangement3", "MapTheme6_Arrangement4" (references non-existent MapTheme9)

"MapTheme7_Arrangement2", "MapTheme7_Arrangement3", "MapTheme7_Arrangement4" (references non-existent MapTheme9)

"MapTheme8_Arrangement2", "MapTheme8_Arrangement3", "MapTheme8_Arrangement4" (references non-existent MapTheme9)

"MapTheme9_Arrangement1", "MapTheme9_Arrangement2", "MapTheme9_Arrangement3", "MapTheme9_Arrangement4" (references non-existent MapTheme9), "MapTheme9_ConstructionMode", "MapTheme9_SubWindow" (references non-existent MapTheme9_FG and MapTheme9_BG)

Again, not sure if this is the issue (seems too simple), but when I listen to the themes in WMP, it is the themes that always fade out suddenly, sometimes just after a turn. Someone in another thread said that it comes back if they access a panel - since the themes for construction mode and such seem fine. I care so much simply because I love the music in the game (especially some of the mapthemes as they are relaxing - and maptheme5 is one of my favs and it cuts out and makes me )