It is nice how [Artist] and [Genre] are "list-interpreted" Fields for display but act like normal string-type fields when tagging in the Panes and Tag AW. It allows you to quickly "fix" groups of files to correct misspellings and whatnot (without having to manually find-and-uncheck incorrect entries).
However, sometimes it is frustrating, and you always have to type them in manually (or import them from metadata lookup services).
Wouldn't it be lovely if you could hold Shift while clicking on the checkbox in the panes to allow you to multi-select on these two (and any other similar "quasi-list-type" fields)?
Perhaps, for bonus points, you could just make [Artist] and [Genre] show in the UI as list-type fields, and add an option to all List-type fields to Require Shift-Click for Multiple Entry (which defaults on for these, and off for others, but which can be changed). That eliminates their "black boxy" nature, adds clarity to how it is used (which confuses users), and also adds utility to other user-defined List-type fields (where one or the other might be appropriate for different people).