I can't be sure if this is a bug, so let me know if otherwise.

1. Situation is I [view] a very long battle from the battle report,
2. I [minimize] the 'windowed' SiS, battle audio stops playing,
3. After some time, I [restore] the 'windowed' SiS, battle continues, thus as the audio, so I [close] the battle,
4. The battle audio continues on for a VERY long time even after the battle screen is gone. <-- is this a bug?

The only solution is to wait out until the audio done its thing or simply close/restart SiS.

Jem wrote:4. The battle audio continues on for a VERY long time even after the battle screen is gone. <-- is this a bug?

It's a bug. The battle audio should terminate with the battle. I'll look into it...