Index: wp-admin/includes/plugin.php
===================================================================
--- wp-admin/includes/plugin.php	(revision 17194)
+++ wp-admin/includes/plugin.php	(working copy)
@@ -88,7 +88,7 @@
 	$plugin_data = get_file_data( $plugin_file, $default_headers, 'plugin' );
 
 	// Site Wide Only is the old header for Network
-	if ( empty( $plugin_data['Network'] ) && ! empty( $plugin_data['_sitewide'] ) ) {
+	if ( empty( $plugin_data['Network'] ) && ! empty( $plugin_data['_sitewide'] ) && is_plugin_active( $plugin_file ) ) {
 		_deprecated_argument( __FUNCTION__, '3.0', sprintf( __( 'The <code>%1$s</code> plugin header is deprecated. Use <code>%2$s</code> instead.' ), 'Site Wide Only: true', 'Network: true' ) );
 		$plugin_data['Network'] = $plugin_data['_sitewide'];
 	}