AFAIK, the music has always looped immediately and indefinitely if you're within its radius. It certainly has since they switched to the .emt format in Planes of Power. There are some fields in the .emt for randomized, delayed looping, but they're only meant for short .wav sound effects like birds chirping. Not for music.
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As for the combat music, I'd guess the original system got broken or patched out some time after they replaced it with mp3 music. The best I've been able to manage with Titanium is setting combattheme1(&2).mp3 to two of the three songs. But that only randomizes on zoning.