JIRA Issues Macro only shows the username from a "Multi User Picker" Custom Field

Steps to Reproduce

1. Create a Custom Field of type "Multi User Picker" in JIRA, name it PIC:
   
2. Associate the field to a screen, and associate the screen to a project
3. Create a user with the display name "test" and username "testuser"
4. Create an issue under a project that has this custom field. Set the PIC to "testuser"
5. Run a search to look for this issue, and make sure that you are able to view the custom field in the JIRA search:
   
6. Click View >> XML , and copy the XML URL
7. In Confluence, insert the JIRA Issues Macro into a page, and set the URL to this XML URL (specify Key, and PIC as the columns to be displayed):
   
8. Refresh the Preview, or Save.

Notice that the PIC customfield displays the user as "testuser" and not "test", as per the search results in JIRA.