Please see my write up here: http://www.somethingunimportant.com/2009/03/04/get-my-patch-added-to-core/ And my ticket/patch here: #2122 Routing with a blank path_prefix causes a bad url to generate - Ruby on Rails - rails
Brief description: When generating routes, a nil :path_prefix is ignored, but a blank :path_prefix ("") is treated like a string with content. In this situation, when the strings are joined an extra slash is added to the beginning of the path.
