Index: wp-admin/includes/screen.php
===================================================================
--- wp-admin/includes/screen.php	(revision 19087)
+++ wp-admin/includes/screen.php	(working copy)
@@ -498,9 +498,11 @@
 			$base .= '-user';
  		}
 
-		if ( isset( self::$_registry[ $id ] ) )
-			return self::$_registry[ $id ];
+		$key = ( $base !== $id ) ? $base . '-' . $id : $id;
 
+		if ( isset( self::$_registry[ $key ] ) )
+			return self::$_registry[ $key ];
+
 		$screen = new WP_Screen();
 		$screen->id         = $id;
 		$screen->base       = $base;
@@ -510,7 +512,7 @@
 		$screen->is_user    = is_user_admin();
 		$screen->is_network = is_network_admin();
 
-		self::$_registry[ $id ] = $screen;
+		self::$_registry[ $key ] = $screen;
 
 		return $screen;
  	}