Okay I believe I identified the source of the problem and this should be a hotfix. Starting on line 1393 in app/models/invoices.php there should be this code: if ($i == 0 && ($dates = $this->Packages->getProrataDates( $service->pricing_id, $service->date_added . 'Z', $service->date_renews . 'Z' )) ) { Change that to: