I can confirm this music bug. Happened to me 5 - 6 times on a 70h playthrough, and only when I was using the speed change (select+square), never happened on normal speed. But only at R06 for now, didn't happen for R06c (but I haven't played much).
Didn't see anything at the log and couldn't replicate it, even with the same enemies. So I didn't bother posting. Seems random and could happen with any random battle.
However it was the victory theme that repeated and played on top of other musics, nonstop.