Problems manually syncing music to my iphone...already did a full restore on the iphone and uninstalled/reinstalled itunes (OSX 10.8)...what happens is I will start with no music on my iphone, I plug in and open itunes, I have the box for "manually manage music" checked (so I can manage all my content since it all wouldn't fit on my iphone), and I can manually transfer music fine. If I disconnect and reconnect again to try and transfer additional music, it automatically tries to sync and transfer my ENTIRE library to my iPhone (manually manage music still being checked), and won't do anything just sitting there stating "preparing device for update" or something like that, and I'd have to erase everything and start all back over. I am not using iTunes Match whatsoever.
Is this on OS X? If so, did you try to delete the plist files?