[4.1] Fix the upgrade path

administrator/components/com_admin/script.php

@@ -97,6 +97,9 @@ public function update($installer)
 
 		// This needs to stay for 2.5 update compatibility
 		$this->deleteUnexistingFiles();
+
+		// Ensure templates are moved to the correct mode
+		$this->fixTemplateMode();
 		$this->updateManifestCaches();
 		$this->updateDatabase();
 		$this->updateAssets($installer);
@@ -8533,4 +8536,37 @@ protected function moveRemainingTemplateFiles()
 			}
 		}
 	}
+
+	/**
+	 * Ensure the core templates are correctly moved to the new mode.
+	 *
+	 * @return  void
+	 *
+	 * @since   __DEPLOY_VERSION__
+	 */
+	protected function fixTemplateMode()
+	{
+		$db = Factory::getDbo();
+
+		array_map(function($template) use ($db)
+		{
+			$clientId = $template === 'atum' ? 1 : 0;
+			$query = $db->getQuery(true)
+				->update($db->quoteName('#__template_styles'))
+				->set($db->quoteName('inheritable') . ' = ' . $db->quote(1))
+				->where($db->quoteName('template') . ' = ' . $db->quote($template))
+				->where($db->quoteName('client_id') . ' = ' . $db->quote($clientId));
+
+			try
+			{
+				$db->setQuery($query)->execute();
+			}
+			catch (Exception $e)
+			{
+				echo Text::sprintf('JLIB_DATABASE_ERROR_FUNCTION_FAILED', $e->getCode(), $e->getMessage()) . '<br>';
+
+				return;
+			}
+		}, ['atum', 'cassiopeia']);
+	}
 }