Index: lib/redmine/wiki_formatting/textile/formatter.rb
===================================================================
--- lib/redmine/wiki_formatting/textile/formatter.rb	(revision 3810)
+++ lib/redmine/wiki_formatting/textile/formatter.rb	(working copy)
@@ -67,7 +67,7 @@
           toc_item = content.gsub(/(\[\[([^\]\|]*)(\|([^\]]*))?\]\])/) { $4 || $2 }
           # sanitizes titles from links
           # see redcloth3.rb, same as "#{pre}#{text}#{post}"
-          toc_item.gsub!(LINK_RE) { $2+$4+$9 }
+          toc_item.gsub!(LINK_RE) { [$2, $4, $9].join }
           # removes styles
           # eg. %{color:red}Triggers% => Triggers
           toc_item.gsub! %r[%\{[^\}]*\}([^%]+)%], '\\1'