This is most probably some old version of this add-on with the preset "Add ""Art Rock"" as the last item to the multi-valued Genre field". With the latest version of the add-on there are updated presets for adding string to multi-item field which don't have mentioned problem: "Add specified string as first item to multi-item <Into Field>..." and "Add specified string as last item to multi-item <Into Field>..." presets.
I said several times in this thread and I will repeat - when I release some new version of this add-on, especially if there is updated syntax of presets, I strongly recommend the following steps:
1. make a backup of your own created presets;
2. uninstall old version of add-on and choose Yes when you asked if you want to remove add-on settings;
3. install new version of add-on;
4. import your own created presets.
In that way you would always have the latest and updated presets. If you don't remove old settings (together with presets), during the installation this script would check the preset's names and if they are same as old ones it would skip their installation, even if they are updated.