Hi once more,

I was missing the action buttons (send mail, see pdf...) in the detail invoice view, so I've made a little hack to display them in tab display.
All is to perform in /administrator/components/com_invoices/views/invoice/tmpl
Add form_actions.php
Update form_tabs.php

If anybody is interested in, feel free to use. Warning : any update of the component will crush form_tab.php