Class methods which call named_scopes lose previous scope (both associations and other scopes)

ActiveRecord models' class methods get added to collections (keeping scope):

    class Post < AR::B
  
      belongs_to :user
    
      def self.wadus
        find(:all, :conditions => { :wadus => "wadus" })
      end
    
    end
  
    user.posts.wadus
    # SELECT * FROM "posts" WHERE ("posts"."wadus" = 'wadus') AND ("posts".user_id = 1)

This works also for named_scopes:

    class Post
      named_scope :starting_with_a, {:conditions => "name LIKE 'a%'"}
    end
  
    Post.starting_with_a.wadus
    # SELECT * FROM "posts" WHERE ("posts"."wadus" = 'wadus') AND (name LIKE 'a%')

But this behaviour breaks if your class method calls one or more named scope:

    class Post < ActiveRecord::Base
  
      belongs_to :user
  
      named_scope :starting_with_a, {:conditions => "name LIKE 'a%'"}  
      named_scope :ending_with_a, {:conditions => "name LIKE '%a'"}
  
      def self.calls_named_scope
        ending_with_a
      end
  
    end
  
    Post.starting_with_a.calls_named_scope
    # SELECT * FROM "posts" WHERE (name LIKE '%a') # loses "name LIKE 'a%'" (from starting_with_a)
    user.posts.calls_named_scope
    # SELECT * FROM "posts" WHERE (name LIKE '%a') # loses "user_id = 1" (from association)

Attached patch includes tests showing this behaviour.