So first things first;
a) UpdateInvoices form, AddItemManuallybutton, ClientSide tab, add BrowseLineItems to Reset list.
This way you press the button, and the list on the window updates.
b) On the TestAddManually Form, BrowseInvoices field, ClientSide tab, add BrowseLineItems to reset list.
Then as you select a row, or edit, the browse, the line items browse updates.
cheers
Bruce