Thank you Gianguido!
This worked for me too. As someone who works a lot with CSS on the web I know all too well how frustrating unwanted caching can be after making updates to a page/app, but I'd never considered that the issue would happen with a desktop app (I guess the iTunes app is probably built on a webkit framework with html and css anyway so kinda makes sense).
Anyway, hopefully Apple devs can watch out for this one in future, perhaps some kind of cache-beater technique can be considered on future releases. I hope Apple at least update their support staff to look out for this issue in future so that they know what they are dealing with (and how to fix it) when someone reports it.