Looking in the code, module routes are only loaded on a request to that module, so module specific routes are only available when a controller in that module has been called.
I don't see any changes in this code between 1.8 and 1.9/dev, so for the moment I'm clueless.
module routes are loaded in Request, when a module controller is called.
It was never contemplated that you would want to get a route from a module from either a global or an other module controller, as that would create a tight coupling between the two, while the idea of modules is that they are self contained.
With the new config key you can decide whether or not you want to load module routes when you load a module.