Index: trunk/core/units/general/cat_event_handler.php
===================================================================
diff -u -N -r7855 -r8012
--- trunk/core/units/general/cat_event_handler.php	(.../cat_event_handler.php)	(revision 7855)
+++ trunk/core/units/general/cat_event_handler.php	(.../cat_event_handler.php)	(revision 8012)
@@ -56,6 +56,9 @@
 			}
 			else {
 				$selected_ids = implode(',', $this->getSelectedIDs($event, true));
+				if (!$selected_ids) {
+					$selected_ids = 0; // when saving newly created item (OnPreCreate -> OnPreSave -> OnSave)
+				}
 			}
 
 			$id_field = $this->Application->getUnitOption($event->Prefix, 'IDField');