@Jesse_ Yesterday i got a TLoZ NSF and the dungeon music was joined with the overworld. It really depends on the guy that ripped the music,if was his intention, or report this issue to the site. I recommend Zophar.net (Best site to get emulated audio files)
@Mr.Sanic Welp, I checked and found this forum: http://forums.nesdev.com/viewtopic.php?p=9220
Scrolled down and found this link: http://www.qmtpro.com/~nes/nsf/battletoads_pcm.zip
It plays all the samples properly compared to the one that's uploaded (Like the title screen and level completed music), but still doesn't have the pause music. I did however find it as its own NSF file elsewhere: http://forums.famitracker.com/viewtopic.php?t=115
Well that's unexpected. Where did you download the NSF from? (The original music pack) i'm not surprised as Battletoads uses DPCM that sounds more clear than standard PCM files. (sorry for editing too much my keyboard is killing me XD)
Battletoads uses plain PCM, which must be cycle timed manually to the PCM port. As you can imagine, this requires music to practically take over the CPU. It also requires NSFs that have an INIT routine that doesn't return, so they can run it indefinitely. This requires an NSF player to support this behavior.