i went into SimpleAudioEngine.cpp and added “alSourcef(iter~~>second~~>source, AL_GAIN, s_effectVolume);” and “alSourcef(s_backgroundSource, AL_GAIN, s_volume);” into the playEffects and playBackgroundMusic functions respectively and the volume issue was resolved. For the case of the bgm, i had to check if bgm is playing, stop it, preload the next bgm to be played, then play it, for the bgm to transit playing correctly
The same problem exists for Blackberry 10. Apparently, my build also play the same background music even when I call playBackgroundMusic() for other files. Stop > Preload> Play solves this issue.