Index: branches/RC/core/units/general/helpers/sections_helper.php
===================================================================
diff -u -N -r11154 -r11353
--- branches/RC/core/units/general/helpers/sections_helper.php	(.../sections_helper.php)	(revision 11154)
+++ branches/RC/core/units/general/helpers/sections_helper.php	(.../sections_helper.php)	(revision 11353)
@@ -92,11 +92,28 @@
 			// 3.
 			foreach ($this->Tree as $section_name => $section_params) {
 				// 3.1. update parent -> children references
-				$this->Tree[ $section_params['parent'] ]['children'][ "{$section_params['priority']}" ] = $section_name;
+				$parent_section = $section_params['parent'];
+				$section_order = "{$section_params['priority']}";
 
+				if (!array_key_exists('children', $this->Tree[$parent_section])) {
+					$this->Tree[$parent_section]['children'] = Array ();
+				}
+
+				if (array_key_exists($section_order, $this->Tree[$parent_section]['children'])) {
+					trigger_error(
+						'Section "<strong>' . $section_name . '</strong>" has replaced section "<strong>' .
+						$this->Tree[$parent_section]['children'][$section_order] .
+						'</strong>" (parent section: "<strong>' . $parent_section .
+						'</strong>"; duplicate priority: <strong>' . $section_order . '</strong>)',
+						E_USER_WARNING
+					);
+				}
+
+				$this->Tree[$parent_section]['children'][$section_order] = $section_name;
+
 				if ($section_params['type'] == stTAB) {
 					// if this is tab, then mark parent section as TabOnly
-					$this->Tree[ $section_params['parent'] ]['tabs_only'] = true;
+					$this->Tree[$parent_section]['tabs_only'] = true;
 				}
 
 				// 3.2. process icons here, because they also can be ajusted