iPod Touch app icons are missing/blank

On my sons 3rd generation iPod Touch, some of the icons of the apps are missing.

I've tried resetting/restoring the iPod, and deleting and reinstalling apps, but still some show with no (that is to say only a white, blank) icon.

The same apps, synced fro the same Mac and account, look fine on my iPhone4.

Apps seem to work fine, it's only the icon that's missing.

iOS is up to date.

Any ideas?

=)

Ole