I've been having an ongoing issue where some movies will delete all of their tags.  I use Tags to create a bunch of custom collections (like "Academy Award Best Picture", "1980s Essentials", "Authors: Steven King", etc).   I add the tags to metadata, then lock the Tags field.  However I am repeatedly having movies unlocking themselves and losing all of their Tags.  I've also noticed sometimes the Tags have become unlocked but the tags I've set are still there (so this appears to have two stages