ITunes :: Embedded Album Artwork Not Displaying In Album List Or Cover Flow

I keep my large music collection on an external drive connected to an Airport Extreme in my home. I've embedded all my album artwork in the music files, and previously all the album artwork was displaying perfectly in iTunes. After upgrading to iTunes 10.5, however, most of my albums are missing the album art in the album list and Cover Flow. I know that the art is still in the file because it shows up in the "Now Playing" box in the lower left corner of the screen. The only way I have found to get the album art to show up again in the album list and Cover Flow is to go through the following steps:  Control-click the first track of an album for which the cover art is not displaying correctly. From the context menu that appears, select Get Info.Click on the Artwork tab, then click Cancel. 

Now the artwork shows up in iTunes in all views. I called Apple Support and asked if there's a faster way to fix the issue with the database. Manually fixing each album for hundreds of albums is no fun. Telling iTunes to Get Album Artwork doesn't work because most of my music was not purchased from iTunes but was ripped from CDs I already own. It's very frustrating because I already spent hours finding and embedding the hi-res album art in my files. I paid extra for Apple products because I expect them to at least avoid corrupting my databases.