I have a 4s with 5.0.1 that after deleting an album that I transfered from cd on my phone that there is many copies that say: unknown artist, unknown album, unkown track name. I back up daily to iCloud and have only used my iPhone to purchase songs/albums. I don't remember exactly which version of iTunes I have at the moment. I also just did an OTA update to 5.1 several hours after this and update iTunes if necessary and see what happens.