Refresh ID3 data

I've been dealing with the same problem, and what I finally did was select all the songs, get info, check the box by "Composer" since I don't care about that tag, then click OK. You might also be able to go to File>Library>Organize Library, and it seems to refresh the tags when you do that. If you've previously organized your library, that option may not be available.

It should update by selecting all the songs then file -> Get info.
If it does not, then go to iTunes prefs - Advanced, untick *Keep iTunes music folder organized*, click OK, then go back and tick it then click OK.

Careful with the "Keep iTunes music folder organized"...

If you currently don't have iTunes managing your folders (I don't), then ticking this option will cause iTunes to move all of your music from wherever it is, into the default iTunes location, using iTunes own folder structure... in my case that would be a DISASTER.

If you already have iTunes managing your folders, then Chris's tip is great; if you manage your own folders, DO NOT tick/untick.

if you manage your own folders, DO NOT tick/untick.

To be clear, I did write untick and then tick.
Yes, if you are managing your own folders differently than iTunes does, then this would change stuff.
However, as I first noted, Get info on the songs should update the iTunes library.