url with some%Fvalue treated differently than some_value

My setup:

passenger via Apache
rails 2.3.2

RailsBaseURI /scala_tour

going to http://www.naildrivin5.com/scala_tour works great

Someone posted a link to http://www.naildrivin5.com/scala_tour and I
get this in my log:

ActionController::RoutingError (No route matches "/scala%5Ftour" with

The browser window renders the underscore. Reloads cause the same
problem. If I copy/paste the link to a new tab, all is well.

What's weird is that Passenger is clearly detecting that scala%5Ftour
should be routed to scala_tour, but then the Rails app gets totally
confused by this.

Anyone experience this? Any ideas how to deal with it (other than
changing the context so the _ isn't there)