iTunes loses entered artist names

I bought a boxed set of compilations, inserted the first CD in the PC drive and when the dialog "Would you like to import ...?" appeared I clicked "Yes". I noticed that only a few of the songs had correct artist names (the rest just showed "Various Artists"), so I dutifully entered the artist names for all the remaining songs, then selected Options →Submit CD Track Names... . I did the same for the next CD in the set. Then I went to play the imported songs and noticed that none of the artist names I had entered were there – they still showed "Various Artists". I put the first CD back in the drive and lo! all the artist names I had entered were there. So my changes had obviously made it to Gracenote and been picked up when I inserted the CD. But why did iTunes not keep them?

The workaround was to delete all the original songs and re-import the CD, but why should it be so hard?

I'm running iTunes 11.0.1.12 on Windows 7.