Rails.application.routes.recognize_path behavior with :action in routes

I am working on a Rails 3.2.21 app and am having an issue with Rails.application.routes.recognize_path and when I have :action in my routes. So for example lets say I have a route:

"/something/:action" => "something#index", action: /index|balloon|hi/

When I do

Rails.application.routes.recognize_path("/something/dude")

instead of getting an exception like I expected it to, I get {controller: "something", action: "dude"}

Why did it ignore my regex constraint?