The expandable view doesn't work as you're saying, there's no way to directly open a bigger version of the artwork by double clicking it. The other method, through the "Edit>Tags" and then double-clicking the artwork does open the bigger version of the picture in another window, as I wanted.
Thanks for the help.
I still don't understand why not just substitute the useless (grayed out) "paste artwork" option for a "show artwork" option which would be much quicker and easier.