COPA posting reversal

We are using ECC6, new GL and COPA. SAP modules SD, MM, FI, CO.

A complex posting has been made with a Sales Order automatically generating a Purchase Order which was GRNd and invoices issued. All of the postings were subsequently cancelled or reversed due to errors and omissions and a new sequence of postings made. This happened several times before the users thought they had got it right!

The end result has been that the Revenue, as shown in the KE30 report, is now zero, but the COGS posting still remains.

Can anyone suggest why the COGS posting would not have been reversed along with the finance postings and how we could resolve this?

Thanks in advance