How to ignore current route values when generating links?

The question is similar to asp.net mvc Html.ActionLink() keeping route value I don't want, but with a twist that makes it more complex.

Starting from a default new MVC3 app, I change the routes to:

routes.MapRoute(
    "r1", // Route name
    "{controller}/{id}/{action}"
);

routes.MapRoute(
    "r2", // Route name
    "{controller}/{action}"
);

Notice that the id comes before the action in the first.

Then in Home\Index.cshtml, I add:

@Url.Action("Index")
@Url.Action("Index", new { id = "blah" })
@Url.Action("Index", new { id = "" })

Now I navigate to /Home/Foo/Index and look at the 3 generated links. I get

1. "/Home/Foo/Index"
2. "/Home/blah/Index"
3. "/Home/Index?id=Foo"

The first two make sense, and are using the first route.

But in the third link, which hits the second route, I don't understand why id=Foo is passed on the query string, given that I explicitly passed an empty id. I would expect it to just generate "/Home/Index".

Can anyone explain that, and suggest how I can get it not to show up?