When do Invoice Distribution lines get populated from Default Dist account?

Can someone please explain when the table AP_INVOICE_DISTRIBUTIONS_ALL gets populated with the distributions based on default distribution account entered in AP Invoice Lines (AP_INVOICE_LINES_ALL)?

The endusers in my company enter invoice lines with the default account in the line or distribution set name at the invoice header level. But, they do not click on the distribution button. Then they run Discoverer reports to check distributions before validating the invoices. This seems to be problem in R12 because the distributions don't seem to be populating unless someone clicks on the Distribution button or when someone validates the invoice. Is this standard functionality?