Created attachment 3123 [details]
Example project demonstrating the issue

Given routes like this:

// Blog home page - Don't include page number in URL for first page
routes.MapRoute(
	name: "BlogHome",
	url: "blog",
	defaults: new { controller = "Home", action = "BlogIndex", page = 1 }
);
routes.MapRoute(
	name: "BlogHomePage",
	url: "blog/page-{page}",
	defaults: new { controller = "Home", action = "BlogIndex" },
	constraints: new { page = @"\d+" }
);

Whenever page=1 is used in the route, it should resolve to /blog, and whenever any other number is used, it should resolve to /blog/page-x. That is, the following Razor (.cshtml) view:
@Url.Action("BlogIndex", "Home", new { page = 1 });
@Url.Action("BlogIndex", "Home", new { page = 2 });

Should display the following:
/blog/page-1
/blog/page-2

This works in Microsoft .NET, but Mono appears to be ignoring the first route and is outputting the following:
/blog/page-1
/blog/page-2

Another issue I've encountered is with the following routes:
routes.MapRoute(
	name: "BlogAdminPostsPublished",
	url: "blog/admin/posts/published",
	defaults: new { controller = "Home", action = "Posts", published = true }
);
routes.MapRoute(
	name: "BlogAdminPostsUnpublished",
	url: "blog/admin/posts/unpublished",
	defaults: new { controller = "Home", action = "Posts", published = false }
);

UrlHelper.Action is not using these routes in Mono - The following:
@Url.Action("Posts", "Home", new { published = true })
@Url.Action("Posts", "Home", new { published = false })

Should output this:
/blog/admin/posts/published
/blog/admin/posts/unpublished

But it is outputting this:
/Home/Posts?published=True
/Home/Posts?published=False

I've attached a test project which demonstrates this issue. This app runs under Mono 3.0 (via XSP) and on Windows via IIS or Cassini.