[Karellen]

I know a lot of users make use of the advancedsettings.xml, but I've never really had any cause to do so until now

I am wondering if you have made an error in the advancedsettings.xml

You posted your code above, can you confirm your file actually has the following code. You may have missed the <advancedsettings> tags.

xml:
<advancedsettings>

   <musiclibrary>

        <artistextraart>

            <arttype>clearlogo</arttype>

        </artistextraart>

        <albumextraart>

            <arttype>discart</arttype>

            <arttype>backcover</arttype>

        </albumextraart>

    </musiclibrary>

</advancedsettings>