Shortcut entries have a Group, Title, and Username (in addition to their implicit link to their base entry).
I have not been able to use the Username field.
If I select a shortcut entry and copy the Username to the clipboard, I get the Username from the base entry (and not that of the shortcut entry, when they differ). This happens whether I use the menu bar or the right-click context menu.
I can open the shortcut entry and select and copy the Username there - but not if the database is read-only.
If there is a need for a Username in shortcut entries (and it seems that I thought so at some point, else I wouldn't have entries with a Username that differs from the base entry), then it should be given "first-class" status - allowing copy to clipboard.
If there is no need for a Username in shortcut entries, it should be deleted from the UI so as not to confuse users.