Apparently, if you have the Master volume slider set to anything less than 100%, the Music and Effect sliders will turn themselves down accordingly after you exit (or next time you enter?) the options screen.
Say, for example, you have the Master slider at 50%, and Effect and Music at 100%. Next time you leave/enter, Master will still be at 50%, but Effect and Music will be down to 50%. Leave and enter again, Master stays at 50%, Effect and Music go down to 25%. Leave and enter again, Master at 50%, Effect and Volume at 12% or 13%.
It appears that this can be temporarily remedied by setting your Master volume to 100%, but it's still kinda messy.
Say, for example, you have the Master slider at 50%, and Effect and Music at 100%. Next time you leave/enter, Master will still be at 50%, but Effect and Music will be down to 50%. Leave and enter again, Master stays at 50%, Effect and Music go down to 25%. Leave and enter again, Master at 50%, Effect and Volume at 12% or 13%.
It appears that this can be temporarily remedied by setting your Master volume to 100%, but it's still kinda messy.