Index: wp-includes/formatting.php
===================================================================
--- wp-includes/formatting.php	(revision 24435)
+++ wp-includes/formatting.php	(working copy)
@@ -2901,7 +2901,7 @@
 
 		case 'illegal_names':
 			if ( ! is_array( $value ) )
-				$value = explode( "\n", $value );
+				$value = explode( ' ', $value );
 
 			$value = array_values( array_filter( array_map( 'trim', $value ) ) );
 
Index: wp-admin/includes/upgrade.php
===================================================================
--- wp-admin/includes/upgrade.php	(revision 24435)
+++ wp-admin/includes/upgrade.php	(working copy)
@@ -1277,6 +1277,16 @@
 	// 3.5
 	if ( $wp_current_db_version < 21823 )
 		update_site_option( 'ms_files_rewriting', '1' );
+
+	// 3.5.2
+	if ( $wp_current_db_version < 30000 ) {
+		$illegal_names = get_site_option( 'illegal_names' );
+		if ( is_array( $illegal_names ) && count( $illegal_names ) === 1 ) {
+			$illegal_name = reset( $illegal_names );
+			$illegal_names = explode( ' ', $illegal_name );
+			update_site_option( 'illegal_names', $illegal_names );
+		}
+	}
 }
 
 // The functions we use to actually do stuff