Index: plugin.php
===================================================================
--- plugin.php	(revision 15865)
+++ plugin.php	(working copy)
@@ -397,7 +397,7 @@
  * @return bool True, if in the active plugins list. False, not in the list.
  */
 function is_plugin_active( $plugin ) {
-	return in_array( $plugin, (array) get_option( 'active_plugins', array() ) ) || is_plugin_active_for_network( $plugin );
+	return ( !is_network_admin() && in_array( $plugin, (array) get_option( 'active_plugins', array() ) ) ) || is_plugin_active_for_network( $plugin );
 }
 
 /**