Media Player Library disappearing? This fixed it for me
First off, I don't sync my library that often, so this didn't adversely affect syncing for me.
Second, I don't use any programs to manage my playlists on my 8525, so this didn't adversely affect me.
I used to lose my library EVERY time I exited Windows Media Player. I had to delete the MSMETADATA folder and update my library every single time I wanted to play music.
However, today I got tired and tried something. Using Resco Explorer, I marked the XMEMediaLibrary.mlb file in the MSMETADATA folder as read-only.
I've reset my device (soft), I've powered off/on, I've quit and killed the wmplayer.exe process. So far, my library has stayed in tact!.
You will have to un-write protect the file to sync directly with WMP or make library modifications on the device.