Continuously updated subform from query

I am creating an invoices database where the charges on each invoice are
recorded in a table of thier own. To display these charges I have a subform
on the Invoices form that is linked to a query that displays all of the
charges for X Invoice number. I can successfully add charges to the table
via a seperate form accessed via command button, but the charges subform on
the Invoice form only updates with the first charge added. Any subsequent
charges are not displayed unles I make the window re-render (such as by going
into design and back to form view. How can I make the query continuously
update that subform to show new charges put on that invoice?

Cory