Ive noticed that it does not happen with music downloaded from itunes... but older albums, and music acquired from sources other than itunes... I had to reset my phone as a new phone, after I spent 40 hours over 3 months, reloading my songs onto the phone. There were no issues for two weeks, and now it is starting again. So, unless it is to do with embedded permissions within music libraries and sources, I'm not sure... but OS7 does delete music indiscriminately off devices... Not everyones though, I have a few friends affected, but many who are not. I am deleting all of my music out of itunes and reloading the cd's into my computer... Over 5000 songs, so this will be time consuming... I'm hoping this works, otherwise, after weeks of searching forums, and speaking to apple representatives... I can tell you that there is no way to fix this that I have found. (Other than a complete reset... set up as new phone etc.)