diff --git a/Makefile b/Makefile
index 3eefe6c3a2f09206138a46fead36e077464583f3..03acdd5d2d9db804bda7d770c90608d3394e9ff1 100644
--- a/Makefile
+++ b/Makefile
@@ -1,7 +1,7 @@
 BASE=ordernumbers
 PLATTFORM=woocommerce
 VENDOR=opentools
-VERSION=1.3.8
+VERSION=1.3.9
 DIR = $(shell pwd)
 SVNDIR=wordpress-plugin-svn
 
@@ -46,4 +46,4 @@ svn: $(SVNDIR)/trunk
 
 svn-release: svn $(SVNDIR)/tags/$(VERSION)
 	rsync -avP $(PLUGINFILES) $(BASICPLUGINFILES) $(TRANSLATIONS) $(SVNDIR)/tags/$(VERSION)
-	
\ No newline at end of file
+	
diff --git a/ordernumbers_woocommerce.php b/ordernumbers_woocommerce.php
index c2c1a152e65cf0fcfa253e823c7405295f01dfad..764a65bc86e2cafb09e5e9c73ecb2f920166dde6 100644
--- a/ordernumbers_woocommerce.php
+++ b/ordernumbers_woocommerce.php
@@ -394,15 +394,18 @@ class OpenToolsOrdernumbers extends OpenToolsOrdernumbersBasic {
 	 * creates a new invoice number if no entry exists in the database)
 	 */
 	function thirdparty_create_invoicenumber($default, $order) {
-		return $this->get_or_create_number($default, $order, 'invoice');
+		if ($this->invoicenumbers_activated()) {
+			return $this->get_or_create_number($default, $order, 'invoice');
+		} else {
+			return $default;
+		}
 	}
 	
 	function thirdparty_get_invoicenumber($default, $orderid) {
 		if ($this->invoicenumbers_activated()) {
 			$_of = new WC_Order_Factory();
 			$order = $_of->get_order($orderid);
-			$number = $this->get_or_create_number($orderid, $order, 'invoice');
-			return $number;
+			return $this->get_number($orderid, $order, 'invoice');
 		} else {
 			return $default;
 		}
@@ -424,9 +427,10 @@ class OpenToolsOrdernumbers extends OpenToolsOrdernumbersBasic {
 	 * Initialize support for WPO WooCommerce PDF Invoices and Packaging Slips
 	 */
 	protected function thirdparty_wpo_wcpdf_init() {
-		// TODO: Wheck whether the woocommerce-pdf-invoices-packing-slips plugin is installed at all
-		add_filter ('wpo_wcpdf_invoice_number', array($this, 'thirdparty_wpo_wcpdf_invoice_number'), 30, 4);
-		add_action ('wpo_wcpdf_process_template_order', array($this, 'thirdparty_wpo_wcpdf_create_number'), 10, 2);
+		// Patch by OpenTools implements the generic interface, so nothing special needs to be done, except to include hints in the plugin config
+// 		add_filter ('wpo_wcpdf_invoice_number', array($this, 'thirdparty_wpo_wcpdf_invoice_number'), 30, 4);
+// 		add_action ('wpo_wcpdf_process_template_order', array($this, 'thirdparty_wpo_wcpdf_create_number'), 10, 2);
+
 		// Disable the invoice number-related controls in the config of the other plugin
 		add_action ('woocommerce_page_wpo_wcpdf_options_page', array($this, 'thirdparty_wpo_wcpdf_remove_options'));
 		// If this plugin is enabled, but invoice numbers are not, display an information message and a link to the config
@@ -439,14 +443,18 @@ class OpenToolsOrdernumbers extends OpenToolsOrdernumbersBasic {
 	 * created in the correct format, no need to format it now again) 
 	 */
 	function thirdparty_wpo_wcpdf_invoice_number($invoice_number, $order_number, $order_id, $order_date) {
-		$_of = new WC_Order_Factory();  
-		$order = $_of->get_order($order_id);
-		$nr = $this->get_or_create_number($order_id, $order, 'invoice');
-		if ($nr == $order_id) {
-			// No number was found, so the default is the order id => reset to invoice number
-			return $invoice_number;
+		if ($this->invoicenumbers_activated() ) {
+			$_of = new WC_Order_Factory();  
+			$order = $_of->get_order($order_id);
+			$nr = $this->get_or_create_number($order_id, $order, 'invoice');
+			if ($nr == $order_id) {
+				// No number was found, so the default is the order id => reset to invoice number
+				return $invoice_number;
+			} else {
+				return $nr;
+			}
 		} else {
-			return $nr;
+			return $invoice_number;
 		}
 	}
 	/**
diff --git a/ordernumbers_woocommerce_basic.php b/ordernumbers_woocommerce_basic.php
index b5e334b23584dea5723d300c4797392ad24bc48e..d3446846a11a82fac6bb2231b00f0b48dece164e 100644
--- a/ordernumbers_woocommerce_basic.php
+++ b/ordernumbers_woocommerce_basic.php
@@ -494,6 +494,11 @@ class OpenToolsOrdernumbersBasic {
 		}
 	}
 	
+	// Only retrieve the number, but do not create it if it doesn't exist:
+	function get_number($default, $order, $type = 'ordernumber') {
+		return get_post_meta( $order->id, $this->ordernumber_meta.$type, true);
+	}
+	
 	/**
 	 * Callback function for Woocommerce to retrieve the ordernumber for an order
 	 * The hook to customize order numbers (requests the order number from the database; 
diff --git a/readme.txt b/readme.txt
index 3d7ffb72afad921befe59ab60c1d213d939a5ee2..70941744c9f61e9ff09a6650dd0eb75185d3d255 100644
--- a/readme.txt
+++ b/readme.txt
@@ -4,7 +4,7 @@ Contributors: opentools
 Tags: WooCommerce, Order numbers, orders
 Requires at least: 4.0
 Tested up to: 4.7
-Stable tag: 1.3.8
+Stable tag: 1.3.9
 License: GPLv3 or later
 License URI: http://www.gnu.org/licenses/gpl.html
 
@@ -78,6 +78,9 @@ The Advanced Ordernumbers for WooCommerce plugin supports some invoicing plugins
 
 == Changelog ==
 
+= 1.3.9 =
+* Fix issues with the WooCommerce PDF Invoices & Packaging Slips plugin (invoice numbers were created even if disabled and before an invoice was actually generated)
+
 = 1.3.8 =
 * Add debug messages to the update system (disabled by default)
 
diff --git a/releases/opentools-woocommerce-ordernumbers-advanced_v1.3.9.zip b/releases/opentools-woocommerce-ordernumbers-advanced_v1.3.9.zip
new file mode 100644
index 0000000000000000000000000000000000000000..374841f03738f20f8d10da880426de9bfbde5c88
Binary files /dev/null and b/releases/opentools-woocommerce-ordernumbers-advanced_v1.3.9.zip differ
diff --git a/releases/opentools-woocommerce-ordernumbers-basic_v1.3.9.zip b/releases/opentools-woocommerce-ordernumbers-basic_v1.3.9.zip
new file mode 100644
index 0000000000000000000000000000000000000000..45d39eb94250300ac07701f241e2aa8113855e2c
Binary files /dev/null and b/releases/opentools-woocommerce-ordernumbers-basic_v1.3.9.zip differ
diff --git a/woocommerce-advanced-ordernumbers.php b/woocommerce-advanced-ordernumbers.php
index a4433bd4b0de578b59796597ccb90a13484c3127..8cfd41551addf743f2cae248c74fec4adde043b9 100644
--- a/woocommerce-advanced-ordernumbers.php
+++ b/woocommerce-advanced-ordernumbers.php
@@ -3,7 +3,7 @@
  * Plugin Name: Woocommerce Advanced Ordernumbers
  * Plugin URI: http://open-tools.net/woocommerce/advanced-ordernumbers-for-woocommerce.html
  * Description: Lets the user freely configure the order numbers in WooCommerce.
- * Version: 1.3.8
+ * Version: 1.3.9
  * Author: Open Tools
  * Author URI: http://open-tools.net
  * Text Domain: woocommerce-advanced-ordernumbers
diff --git a/woocommerce-basic-ordernumbers.php b/woocommerce-basic-ordernumbers.php
index 64c503bff3ae4796bc7bf93c281c855bafd003e4..4345d19c2564422e7e92e12d02b0d5163fcfce50 100644
--- a/woocommerce-basic-ordernumbers.php
+++ b/woocommerce-basic-ordernumbers.php
@@ -3,7 +3,7 @@
  * Plugin Name: WooCommerce Basic Ordernumbers
  * Plugin URI: http://open-tools.net/woocommerce/advanced-ordernumbers-for-woocommerce.html
  * Description: Configure WooCommerce ordernumbers to have a running counter and arbitrary, fixed text (prefix / postfix).
- * Version: 1.3.8
+ * Version: 1.3.9
  * Author: Open Tools
  * Author URI: http://open-tools.net
  * Text Domain: woocommerce-advanced-ordernumbers