Rails 3路由：Globbing打破隐式（。：format）参数

Question

在Rails 3（.0.4）中，用户定义的路由在末尾有一个隐式（。：格式）参数（注意“as HTML / XML”）：

match "/~(/:foo)" => "categories#index"

Started GET "/~/bar" for 127.0.0.1 at 2011-02-12 08:45:00 +0000
  Processing by CategoriesController#index as HTML
  Parameters: {"foo"=>"bar"}

Started GET "/~/bar.xml" for 127.0.0.1 at 2011-02-12 08:45:00 +0000
  Processing by CategoriesController#index as XML
  Parameters: {"foo"=>"bar"}

然而，通过globbing，这不再起作用了：

match "/~(/*foo)" => "categories#index"

Started GET "/~/bar" for 127.0.0.1 at 2011-02-12 08:48:14 +0000
  Processing by CategoriesController#index as HTML
  Parameters: {"foo"=>"bar"}

Started GET "/~/bar.xml" for 127.0.0.1 at 2011-02-12 08:48:19 +0000
  Processing by CategoriesController#index as HTML
  Parameters: {"foo"=>"bar.xml"}

为什么不，我怎样才能让它发挥作用？