Beside this ...
Actions
... there is also the possibility to create a multi value GENRE tag-field, using the action "Format value" on the tag-field GENRE with a Formatstring containig values, which are separated by the "Double Slash" separator, e. g. 'Rock\\Trash'.
Use the dialog "Extended Tag View..." to display all tag-fields with their content.
DD.20110903.1945.CEST