I bought lumia 720 abut 2 weeks ago, the volume function was working fine then. i have been facing the same problem since i started listening to music in 'NOKIA MIX RADIO' as now the music store is updated to this. i had downloaded all my songs from the store, but the volume function is not working while the song is running, i have to change the song to change the volume. and the problem is coming in all the songs except a few in which the volume is functioning. the audio settings (dolby effect and audio leveling) are not solving the issue.
i have noticed one thing that the problem is not coming if i play my downloaded songs from 'my music' option in 'nokia mix radio', but it is coming when i play them from 'music and videos'.