is it possible to import a single credit note matched to multiple invoices via autoinvoice?

I am populating the interface tables with a single credit memo and referencing multiple invoices and lines via the reference... columns.  However, when I run autoinvoice it rejects the CM as being a duplicate invoice number.  The CM number is manual and I have confirmed that it is unique for the source, i.e. it doesn't exist in the core tables, nor are there any other records in the interface table for the same CM.

If I import the CM as matched to a single invoice, then it works fine.

Any pointers would be great!

Thanks

Ringo