I’m using the free version of ACF.
When I use the export function, all registered users of my blog are part of the export file advanced-custom-field-export.xml.
I need to assign all authors when I want to import the fields to my other blog. This is very time-consuming.
If I delete the users at the beginning <wp:author>…</wp:author> of the xml file, I only need to assign the creators and not all. This should be the default behaviour.
I’m not sure if this is a bug, but I have no idea why I should import users who have never created or changed anything in the field groups.
The XML export for ACF fields in version 4 basically uses the standard WP xml export tool. The file you get is the same file that you’d get if you go to Tools => Export, select “Field Groups” and download the export.
At this point I doubt that any improvements to ACF4 are going to be made. The developer is working on getting a free version of ACF5 released. But you can try submitting the bug report through by opening a new support ticket https://support.advancedcustomfields.com/new-ticket/