iTunes Match Album Artwork Missing

All of my albums have artwork associated with them in iTunes. I just upgraded to iTunes to include Match. However, when I enable Match on my iPad, I am missing about 15% of my album artwork images.

Sometimes, if I select an album to play it on my iPad, I can get the album artwork to magically appear (and I hope it's persistent). However, there are some albums that, though they show up on my desktop iTunes, the images simply won't load on my iPad iTunes.

Any suggestions or is this normal? I assumed that it would "just work" like Apple products typically do! 😉