I am dealing with two different issues at the moment with my library.
1. I have been ripping some vinyl to FLAC and when I do so I have a careful naming convention that I follow:
folder = [artist] - [album]
file= [Track#] [Name ([Year])
But when I use the fill properties from file name function, the results are jumbled and don't match the original file names. Three or four songs will have the exact same name, some of the artist properties are wrong and the track numbers are not filled out. If I then try to rename one of the incorrect files using the function again MC treats the files as if they are correct and won't fix the errors. This happens even though there is a mismatch between the properties and the file name.
2. MC has gone and renamed the albums on a large number of my files where the song title and artist are the same on both files. Thus for example, if I have 'London Calling' by The Clash on the album of that title and on the best of, the album and track number have both been changed on one album to become identical to the other. Thus the best of has two entries for London Calling. I only noticed because the album art remained for the correct album.