Billing/invoice and attached files?

[magsnus76 at gmail.com]

Hi everyone! 

Is there a way to use the new feature of attaching files to transactions with 
invoices and bills generated from the business module?If i try to attach a file 
to an transaction that are generated when i post a bill i get a message that 
the transaction is locked and that i can try to unpost the bill but if i do so 
there i no transaction that i can associate the file with.