Hello,
That attribute is required for the proper functioning of LibreOffice 4.3 and newest (and also some versions of OpenOffice). That's why we requested you to use LibreOffice instead of OpenOffice as conversion plugin.
If you're using OpenOffice, the default conversion plugin is LibreOffice since phpdocx 4.5, it's better to remove it. We're going to add a new option to avoid the use of that attribute when working with OpenOffice by default.
We have sent you an email with a minor change in the class to find an automatic general fix without adding a new option.
Regards.