AutoInvoice - DFF not required but still returns error

Hi all,

We're using autoinvoice to import invoice from other system.  We use several DFFs at the line (interface_line_attributes - context specific) as well as the header level (Header_attributes - using Global Data Elements). 

A couple of these DFFs are not mandatory - they're extra fields that can be used whenever we need to store more information on the transaction, otherwise they can be left blank.  I have set them as not required (Required checkbox on the value set is unchecked), but whenever I leave these DFFs blank the system throws an error "All enabled segments of Transaction Flexfield must have a value".  Is there any way to resolve this.