diff --git a/htdocs/compta/facture.php b/htdocs/compta/facture.php
index 25d032982a9..b3d365650b5 100644
--- a/htdocs/compta/facture.php
+++ b/htdocs/compta/facture.php
@@ -486,14 +486,21 @@ else if ($action == 'confirm_canceled' && $confirm == 'yes') {
 // Convertir en reduc
 else if ($action == 'confirm_converttoreduc' && $confirm == 'yes' && $user->rights->facture->creer)
 {
-	$db->begin();
-
 	$object->fetch($id);
 	$object->fetch_thirdparty();
 	$object->fetch_lines();
 
-	if (empty($object->paye))	// protection against multiple submit
+	// Check if there is already a discount (protection to avoid duplicate creation when resubmit post)
+	$discountcheck=new DiscountAbsolute($db);
+	$result=$discountcheck->fetch(0,$object->id);
+
+	$canconvert=0;
+	if ($object->type == Facture::TYPE_DEPOSIT && $object->paye == 1 && empty($discountcheck->id)) $canconvert=1;	// we can convert deposit into discount if deposit is payed completely and not already converted (see real condition into condition used to show button converttoreduc)
+	if ($object->type == Facture::TYPE_CREDIT_NOTE && $object->paye == 0 && empty($discountcheck->id)) $canconvert=1;	// we can convert credit note into discount if credit note is not payed back and not already converted and amount of payment is 0 (see real condition into condition used to show button converttoreduc)
+	if ($canconvert)
 	{
+		$db->begin();
+
 		// Boucle sur chaque taux de tva
 		$i = 0;
 		foreach ($object->lines as $line) {
@@ -1745,9 +1752,10 @@ if ($action == 'update_extras') {
 		$action = 'edit_extras';
 }
 
+
 /*
  * View
-*/
+ */
 
 $form = new Form($db);
 $formother = new FormOther($db);
@@ -1941,10 +1949,12 @@ if ($action == 'create')
 		$options .= '</option>';
 	}
 
-	$facids = $facturestatic->list_qualified_avoir_invoices($soc->id);
-	if ($facids < 0) {
-		dol_print_error($db, $facturestatic);
-		exit();
+	// Show link for credit note
+	$facids=$facturestatic->list_qualified_avoir_invoices($soc->id);
+	if ($facids < 0)
+	{
+		dol_print_error($db,$facturestatic);
+		exit;
 	}
 	$optionsav = "";
 	$newinvoice_static = new Facture($db);
@@ -3277,10 +3287,11 @@ if ($action == 'create')
 			}
 
 			// Reopen a standard paid invoice
-			if (($object->type == Facture::TYPE_STANDARD || $object->type == Facture::TYPE_REPLACEMENT) && ($object->statut == Facture::TYPE_CREDIT_NOTE || $object->statut == Facture::TYPE_DEPOSIT) && $user->rights->facture->creer) 			// A paid
-			                                                                                                                                   // invoice
-			                                                                                                                                   // (partially or
-			                                                                                                                                   // completely)
+			if ((($object->type == Facture::TYPE_STANDARD || $object->type == Facture::TYPE_REPLACEMENT)
+				|| ($object->type == Facture::TYPE_CREDIT_NOTE && empty($discount->id))
+				|| ($object->type == Facture::TYPE_DEPOSIT && empty($discount->id)))
+				&& ($object->statut == 2 || $object->statut == 3)
+				&& $user->rights->facture->creer)				// A paid invoice (partially or completely)
 			{
 				if (! $objectidnext && $object->close_code != 'replaced') 				// Not replaced by another invoice
 				{
@@ -3339,30 +3350,47 @@ if ($action == 'create')
 			// Reverse back money or convert to reduction
 			if ($object->type == Facture::TYPE_CREDIT_NOTE || $object->type == Facture::TYPE_DEPOSIT) {
 				// For credit note only
-				if ($object->type == Facture::TYPE_CREDIT_NOTE && $object->statut == 1 && $object->paye == 0 && $user->rights->facture->paiement) {
-					print '<div class="inline-block divButAction"><a class="butAction" href="paiement.php?facid=' . $object->id . '&amp;action=create">' . $langs->trans('DoPaymentBack') . '</a></div>';
+				if ($object->type == Facture::TYPE_CREDIT_NOTE && $object->statut == 1 && $object->paye == 0 && $user->rights->facture->paiement)
+				{
+					if ($resteapayer == 0)
+					{
+						print '<div class="inline-block divButAction"><span class="butActionRefused" title="'.$langs->trans("DisabledBecauseRemainderToPayIsZero").'">'.$langs->trans('DoPaymentBack').'</span></div>';
+					}
+					else
+					{
+						print '<div class="inline-block divButAction"><a class="butAction" href="paiement.php?facid='.$object->id.'&amp;action=create">'.$langs->trans('DoPaymentBack').'</a></div>';
+					}
 				}
+
 				// For credit note
 				if ($object->type == Facture::TYPE_CREDIT_NOTE && $object->statut == 1 && $object->paye == 0 && $user->rights->facture->creer && $object->getSommePaiement() == 0) {
 					print '<div class="inline-block divButAction"><a class="butAction" href="' . $_SERVER ["PHP_SELF"] . '?facid=' . $object->id . '&amp;action=converttoreduc">' . $langs->trans('ConvertToReduc') . '</a></div>';
 				}
 				// For deposit invoice
-				if ($object->type == Facture::TYPE_DEPOSIT && $object->statut == 2 && $resteapayer == 0 && $user->rights->facture->creer && empty($discount->id)) {
-					print '<div class="inline-block divButAction"><a class="butAction" href="' . $_SERVER ["PHP_SELF"] . '?facid=' . $object->id . '&amp;action=converttoreduc">' . $langs->trans('ConvertToReduc') . '</a></div>';
+				if ($object->type == Facture::TYPE_DEPOSIT && $object->paye == 1 && $resteapayer == 0 && $user->rights->facture->creer && empty($discount->id))
+				{
+					print '<div class="inline-block divButAction"><a class="butAction" href="'.$_SERVER["PHP_SELF"].'?facid='.$object->id.'&amp;action=converttoreduc">'.$langs->trans('ConvertToReduc').'</a></div>';
 				}
 			}
 
-			// Classify paid (if not deposit and not credit note. Such invoice are "converted")
-			if ($object->statut == 1 && $object->paye == 0 && $user->rights->facture->paiement && (($object->type != Facture::TYPE_CREDIT_NOTE && $object->type != Facture::TYPE_DEPOSIT && $resteapayer <= 0) || ($object->type == Facture::TYPE_CREDIT_NOTE && $resteapayer >= 0))) {
-				print '<div class="inline-block divButAction"><a class="butAction" href="' . $_SERVER ['PHP_SELF'] . '?facid=' . $object->id . '&amp;action=paid">' . $langs->trans('ClassifyPaid') . '</a></div>';
+			// Classify paid
+			if ($object->statut == 1 && $object->paye == 0 && $user->rights->facture->paiement && (($object->type != Facture::TYPE_CREDIT_NOTE && $object->type != Facture::TYPE_DEPOSIT && $resteapayer <= 0) || ($object->type == Facture::TYPE_CREDIT_NOTE && $resteapayer >= 0))
+				|| ($object->type == Facture::TYPE_DEPOSIT && $object->paye == 0 && $resteapayer == 0 && $user->rights->facture->paiement && empty($discount->id))
+			)
+			{
+				print '<div class="inline-block divButAction"><a class="butAction" href="'.$_SERVER['PHP_SELF'].'?facid='.$object->id.'&amp;action=paid">'.$langs->trans('ClassifyPaid').'</a></div>';
 			}
 
 			// Classify 'closed not completely paid' (possible si validee et pas encore classee payee)
-			if ($object->statut == 1 && $object->paye == 0 && $resteapayer > 0 && $user->rights->facture->paiement) {
-				if ($totalpaye > 0 || $totalcreditnotes > 0) {
+			if ($object->statut == 1 && $object->paye == 0 && $resteapayer > 0 && $user->rights->facture->paiement)
+			{
+				if ($totalpaye > 0 || $totalcreditnotes > 0)
+				{
 					// If one payment or one credit note was linked to this invoice
 					print '<div class="inline-block divButAction"><a class="butAction" href="' . $_SERVER ['PHP_SELF'] . '?facid=' . $object->id . '&amp;action=paid">' . $langs->trans('ClassifyPaidPartially') . '</a></div>';
-				} else {
+				}
+				else
+				{
 					if ($objectidnext) {
 						print '<div class="inline-block divButAction"><span class="butActionRefused" title="' . $langs->trans("DisabledBecauseReplacedInvoice") . '">' . $langs->trans('ClassifyCanceled') . '</span></div>';
 					} else {
@@ -3372,19 +3400,23 @@ if ($action == 'create')
 			}
 
 			// Clone
-			if (($object->type == Facture::TYPE_STANDARD || $object->type == Facture::TYPE_DEPOSIT || $object->type == Facture::TYPE_PROFORMA) && $user->rights->facture->creer) {
+			if (($object->type == Facture::TYPE_STANDARD || $object->type == Facture::TYPE_DEPOSIT || $object->type == Facture::TYPE_PROFORMA) && $user->rights->facture->creer)
+			{
 				print '<div class="inline-block divButAction"><a class="butAction" href="' . $_SERVER ['PHP_SELF'] . '?facid=' . $object->id . '&amp;action=clone&amp;object=invoice">' . $langs->trans("ToClone") . '</a></div>';
 			}
 
 			// Clone as predefined
-			if (($object->type == Facture::TYPE_STANDARD || $object->type == Facture::TYPE_DEPOSIT || $object->type == Facture::TYPE_PROFORMA) && $object->statut == 0 && $user->rights->facture->creer) {
-				if (! $objectidnext) {
+			if (($object->type == Facture::TYPE_STANDARD || $object->type == Facture::TYPE_DEPOSIT || $object->type == Facture::TYPE_PROFORMA) && $object->statut == 0 && $user->rights->facture->creer)
+			{
+				if (! $objectidnext)
+				{
 					print '<div class="inline-block divButAction"><a class="butAction" href="facture/fiche-rec.php?facid=' . $object->id . '&amp;action=create">' . $langs->trans("ChangeIntoRepeatableInvoice") . '</a></div>';
 				}
 			}
 
 			// Delete
-			if ($user->rights->facture->supprimer) {
+			if ($user->rights->facture->supprimer)
+			{
 				if (! $object->is_erasable()) {
 					print '<div class="inline-block divButAction"><a class="butActionRefused" href="#" title="' . $langs->trans("DisabledBecauseNotErasable") . '">' . $langs->trans('Delete') . '</a></div>';
 				} else if ($objectidnext) {
@@ -3403,7 +3435,8 @@ if ($action == 'create')
 	}
 	print '<br>';
 
-	if ($action != 'prerelance' && $action != 'presend') {
+	if ($action != 'prerelance' && $action != 'presend')
+	{
 		print '<div class="fichecenter"><div class="fichehalfleft">';
 		print '<a name="builddoc"></a>'; // ancre