exception notifier and RoutingError

I'm running Rails, Rev.4306, which was edge when I froze my application. I
installed the exception notifier plugin (great plugin!), and it works fine
if I have an action that raises an exception. However, if I type a bad URL,
I still wind up at the beautiful white screen:

Routing Error

Recognition failed for "/zoo"

My log shows that the error occurred, but for some reason was not trapped.
Any thoughts as to why?

Thanks

ActionController::RoutingError (Recognition failed for "/zoo"):
    /vendor/rails/actionpack/lib/action_controller/routing.rb:545:in
`recognition_failed'
    /vendor/rails/actionpack/lib/action_controller/routing.rb:535:in
`recognize!'
    /vendor/rails/railties/lib/dispatcher.rb:38:in `dispatch'
   
/usr/local/lib/ruby/gems/1.8/gems/mongrel-0.3.13.3/lib/mongrel/rails.rb:73:in
`process'
    /usr/local/lib/ruby/gems/1.8/gems/mongrel-0.3.13.3/lib/mongrel.rb:551:in
`process_client'
    /usr/local/lib/ruby/gems/1.8/gems/mongrel-0.3.13.3/lib/mongrel.rb:550:in
`process_client'
    /usr/local/lib/ruby/gems/1.8/gems/mongrel-0.3.13.3/lib/mongrel.rb:636:in
`run'
    /usr/local/lib/ruby/gems/1.8/gems/mongrel-0.3.13.3/lib/mongrel.rb:636:in
`run'
    /usr/local/lib/ruby/gems/1.8/gems/mongrel-0.3.13.3/lib/mongrel.rb:625:in
`run'
    /usr/local/lib/ruby/gems/1.8/gems/mongrel-0.3.13.3/lib/mongrel.rb:956:in
`run'
    /usr/local/lib/ruby/gems/1.8/gems/mongrel-0.3.13.3/lib/mongrel.rb:955:in
`run'
   
/usr/local/lib/ruby/gems/1.8/gems/mongrel-0.3.13.3/bin/mongrel_rails:127:in
`run'
   
/usr/local/lib/ruby/gems/1.8/gems/mongrel-0.3.13.3/lib/mongrel/command.rb:199:in
`run'
    /usr/local/lib/ruby/gems/1.8/gems/mongrel-0.3.13.3/bin/mongrel_rails:235
    /usr/local/bin/mongrel_rails:18