The weird thing, though, is that I've not changed any backgrounds at all. All I edit are a couple of dialogues per level, so it's only the game text that should be changed, and there shouldn't be any reason for the music to change :/
The music that is played seems to be completely dependant on how I've edited the text fields, because if I change the text again the music could switch to yet another midi. For example, I've had the level called "nmkin" (North No.1 Mako Reactor upper floor, from the beginning of the game) play everything from Don of the Slums to Steal the Tiny Bronco, when all I've done is translate some of the dialogues into Swedish :)
Now that I think of it, could there be problems because I haven’t “packed†the lgp library? Read something about extracting all files and then put them all together to get rid of any gaps that could cause the file size to increase (which it does for me), but I never quite understood what it meant and thought it would work without doing so. I tried packing inside of Cosmo once, but then my lgp lib got corrupt so perhaps I was doing something wrong.