Make sure headers are properly cleared and set.

lib/shopify_api/resources/base.rb

@@ -8,21 +8,27 @@ module ShopifyAPI
                                   "ActiveResource/#{ActiveResource::VERSION::STRING}",
                                   "Ruby/#{RUBY_VERSION}"].join(' ')
 
+    class << self
+      def headers
+        if defined?(@headers)
+          @headers
+        elsif superclass != Object && superclass.headers
+          superclass.headers
+        else
+          @headers ||= {}
+        end
+      end
 
+      def activate_session(session)
+        self.site = session.site
+        self.headers.merge!('X-Shopify-Access-Token' => session.token)
+      end
 
-    def self.activate_session(session)
-      self.site = session.site
-      ActiveResource::Base.site = session.site
-      self.headers.merge!('X-Shopify-Access-Token' => session.token)
-      ActiveResource::Base.headers.merge!('X-Shopify-Access-Token' => session.token)
-    end
-
-    def self.clear_session
-      self.site = nil
-      ActiveResource::Base.site = nil
-      self.headers.delete('X-Shopify-Access-Token')
-      ActiveResource::Base.headers.delete('X-Shopify-Access-Token')
-    end                                  
+      def clear_session
+        self.site = nil
+        self.headers.delete('X-Shopify-Access-Token')
+      end
+    end                  
 
     private
     def only_id