Fix incorrect filtering of custom blocks from drop-down list

root/includes/acp/acp_portal.php

@@ -857,6 +857,8 @@ class acp_portal
 							}
 							
 							// do we want to add the module to the side columns or to the center columns?
+							if ($module_class != 'custom')
+							{
 								if (in_array($column_string, array('left', 'right')))
 								{
 									// does the module already exist in the side columns?
@@ -877,6 +879,7 @@ class acp_portal
 										continue;
 									}
 								}
+							}
 							
 							if (!class_exists($class))
 							{