Whenever you play a game from the HDD, the CD track will either:
1. stop when the track ends and never come back on or
2. if you die in certain games, the music will stop playing when you continue and it never comes back on.
In some games, the sound glitching is just plain weird. For Dracula X Rondo of Blood, the boss music will keep playing through the victory tune after a boss is defeated. Or play Mugen Senshi Valis I, Valis II, or Valis III. Die on purpose. Wait for the music to come back on....then keep waiting forever.
These glitches with music playing over itself and stopping completely will only affect CD based games. The thing is, a huge part of the novelty and value of even playing CD based games on PC Engine is due to each game's CD soundtrack.
I just want to get this out there to the master coders so that it can be fixed. The whole emulation community will really appreciate it.