diff --git a/lib/couchrest/mixins/properties.rb b/lib/couchrest/mixins/properties.rb
index e7a6303..bc83571 100644
--- a/lib/couchrest/mixins/properties.rb
+++ b/lib/couchrest/mixins/properties.rb
@@ -37,37 +37,55 @@ module CouchRest
       def cast_keys
         return unless self.class.properties
         self.class.properties.each do |property|
-          next unless property.casted
-          key = self.has_key?(property.name) ? property.name : property.name.to_sym
-          # Don't cast the property unless it has a value
-          next unless self[key]
-          target = property.type
-          if target.is_a?(Array)
-            klass = ::CouchRest.constantize(target[0])
-            arr = self[key].collect do |value|
-              # Auto parse Time objects
-              obj = ( (property.init_method == 'new') && klass == Time) ? Time.parse(value) : klass.send(property.init_method, value)
-              obj.casted_by = self if obj.respond_to?(:casted_by)
-              obj.document_saved = true if obj.respond_to?(:document_saved)
-              obj
-            end
-            self[property.name] = target[0] != 'String' ? CastedArray.new(arr) : arr
-          else
-            # Auto parse Time objects
-            self[property.name] = if ((property.init_method == 'new') && target == 'Time') 
-              self[key].is_a?(String) ? Time.parse(self[key].dup) : self[key]
-            else
-              # Let people use :send as a Time parse arg
-              klass = ::CouchRest.constantize(target)
-              klass.send(property.init_method, self[key].dup)
-            end
-            self[property.name].casted_by = self if self[property.name].respond_to?(:casted_by)
-            self[property.name].document_saved = true if self[property.name].respond_to?(:document_saved)
-          end
-          self[property.name].casted_by = self if self[property.name].respond_to?(:casted_by)
+          cast_property(property)
         end
       end
       
+      def cast_property(property)
+        return unless property.casted
+        key = self.has_key?(property.name) ? property.name : property.name.to_sym
+        # Don't cast the property unless it has a value
+        return unless self[key]
+        target = property.type
+        if target.is_a?(Array)
+          klass = ::CouchRest.constantize(target[0])
+          arr = self[key].dup.collect do |value|
+            unless value.instance_of?(klass)
+              value = convert_property_value(property, klass, value)
+            end
+            associate_casted_to_parent(value)
+            value
+          end
+          self[key] = target[0] != 'String' ? CastedArray.new(arr) : arr
+        else
+          klass = ::CouchRest.constantize(target)
+          unless self[key].instance_of?(klass)
+            self[key] = convert_property_value(property, klass, self[property.name])
+          end
+          associate_casted_to_parent(self[property.name])
+        end
+      end
+      
+      def associate_casted_to_parent(casted)
+        casted.casted_by = self if casted.respond_to?(:casted_by)
+        casted.document_saved = true if casted.respond_to?(:document_saved)
+      end
+      
+      def convert_property_value(property, klass, value)
+        if ((property.init_method == 'new') && klass.to_s == 'Time') 
+          value.is_a?(String) ? Time.parse(value.dup) : value
+        else
+          klass.send(property.init_method, value.dup)
+        end
+      end
+      
+      def cast_property_by_name(property_name)
+        return unless self.class.properties
+        property = self.class.properties.detect{|property| property.name == property_name}
+        return unless property
+        cast_property(property)
+      end
+      
       module ClassMethods
         
         def property(name, options={})
@@ -108,28 +126,17 @@ module CouchRest
 
           # defines the setter for the property (and optional aliases)
           def create_property_setter(property)
-            meth = property.name
+            property_name = property.name
             class_eval <<-EOS
-              def #{meth}=(value)
-                if #{property.casted} && value.is_a?(Array)
-                  arr = CastedArray.new
-                  arr.casted_by = self
-                  value.each do |v|
-                    obj = #{property.type}.new(v)
-                    arr << obj
-                  end
-                  value = arr
-                elsif #{property.casted}
-                  value = #{property.type}.new(v)
-                  value.casted_by = self if value.respond_to?(:casted_by)
-                end
-                self['#{meth}'] = value
+              def #{property_name}=(value)
+                self['#{property_name}'] = value
+                cast_property_by_name('#{property_name}')
               end
             EOS
 
             if property.alias
               class_eval <<-EOS
-                alias #{property.alias.to_sym}= #{meth.to_sym}=
+                alias #{property.alias.to_sym}= #{property_name.to_sym}=
               EOS
             end
           end
diff --git a/lib/couchrest/more/extended_document.rb b/lib/couchrest/more/extended_document.rb
index bd7377f..a3e941b 100644
--- a/lib/couchrest/more/extended_document.rb
+++ b/lib/couchrest/more/extended_document.rb
@@ -51,9 +51,6 @@ module CouchRest
       end
     end
     
-
-    
-    
     # Automatically set <tt>updated_at</tt> and <tt>created_at</tt> fields
     # on the document whenever saving occurs. CouchRest uses a pretty
     # decent time format by default. See Time#to_json
@@ -62,16 +59,13 @@ module CouchRest
         property(:updated_at, :read_only => true, :cast_as => 'Time', :auto_validation => false)
         property(:created_at, :read_only => true, :cast_as => 'Time', :auto_validation => false)
         
-        def created_at=(ignored); end
-        def updated_at=(ignored); end
-        
         save_callback :before do |object|
           object['updated_at'] = Time.now
           object['created_at'] = object['updated_at'] if object.new?
         end
       EOS
     end
-  
+    
     # Name a method that will be called before the document is first saved,
     # which returns a string to be used for the document's <tt>_id</tt>.
     # Because CouchDB enforces a constraint that each id must be unique,
@@ -130,10 +124,15 @@ module CouchRest
     # for each key. It doesn't save the document at the end. Raises a NoMethodError if the corresponding methods are
     # missing. In case of error, no attributes are changed.    
     def update_attributes_without_saving(hash)
-      hash.each do |k, v|
+      # remove attributes that cannot be updated, silently ignoring them
+      # which matches Rails behavior when, for instance, setting created_at.
+      # make a copy, we don't want to change arguments
+      attrs = hash.dup
+      %w[_id _rev created_at updated_at].each {|attr| attrs.delete(attr)}
+      attrs.each do |k, v|
         raise NoMethodError, "#{k}= method not available, use property :#{k}" unless self.respond_to?("#{k}=")
       end      
-      hash.each do |k, v|
+      attrs.each do |k, v|
         self.send("#{k}=",v)
       end
     end
diff --git a/spec/couchrest/more/casted_extended_doc_spec.rb b/spec/couchrest/more/casted_extended_doc_spec.rb
index 51afd77..eef1541 100644
--- a/spec/couchrest/more/casted_extended_doc_spec.rb
+++ b/spec/couchrest/more/casted_extended_doc_spec.rb
@@ -43,16 +43,14 @@ describe "assigning a value to casted attribute after initializing an object" do
     @car.driver.should be_nil
   end
   
-  # Note that this isn't casting the attribute, it's just assigning it a value
-  # (see "should not cast attribute")
   it "should let you assign the value" do
     @car.driver = @driver
     @car.driver.name.should == 'Matt'
   end
   
-  it "should not cast attribute" do
+  it "should cast attribute" do
     @car.driver = JSON.parse(JSON.generate(@driver))
-    @car.driver.should_not be_instance_of(Driver)
+    @car.driver.should be_instance_of(Driver)
   end
 
 end
diff --git a/spec/couchrest/more/casted_model_spec.rb b/spec/couchrest/more/casted_model_spec.rb
index 029e294..a6c5aa3 100644
--- a/spec/couchrest/more/casted_model_spec.rb
+++ b/spec/couchrest/more/casted_model_spec.rb
@@ -284,7 +284,8 @@ describe CouchRest::CastedModel do
     before :each do
       reset_test_db!
       @cat = Cat.new(:name => 'Sockington')
-      @cat.favorite_toy = CatToy.new(:name => 'Catnip Ball')
+      @favorite_toy = CatToy.new(:name => 'Catnip Ball')
+      @cat.favorite_toy = @favorite_toy
       @cat.toys << CatToy.new(:name => 'Fuzzy Stick')
     end
     
@@ -294,6 +295,7 @@ describe CouchRest::CastedModel do
     end
     
     it "should be true after assignment" do
+      @cat.should be_new
       @cat.favorite_toy.should be_new
       @cat.toys.first.should be_new
     end
@@ -336,6 +338,7 @@ describe CouchRest::CastedModel do
     
     it "should reference the top document for" do
       @course.base_doc.should === @course
+      @professor.casted_by.should === @course
       @professor.base_doc.should === @course
       @cat.base_doc.should === @course
       @toy1.base_doc.should === @course
@@ -343,6 +346,7 @@ describe CouchRest::CastedModel do
     end
     
     it "should call setter on top document" do
+      @toy1.base_doc.should_not be_nil
       @toy1.base_doc.title = 'Tom Foolery'
       @course.title.should == 'Tom Foolery'
     end
diff --git a/spec/couchrest/more/extended_doc_spec.rb b/spec/couchrest/more/extended_doc_spec.rb
index d4100bf..403eedd 100644
--- a/spec/couchrest/more/extended_doc_spec.rb
+++ b/spec/couchrest/more/extended_doc_spec.rb
@@ -118,7 +118,22 @@ describe "ExtendedDocument" do
       @art.update_attributes_without_saving('date' => Time.now, :title => "super danger")
       @art['title'].should == "super danger"
     end
-    
+    it "should silently ignore _id" do
+      @art.update_attributes_without_saving('_id' => 'foobar')
+      @art['_id'].should_not == 'foobar'
+    end
+    it "should silently ignore _rev" do
+      @art.update_attributes_without_saving('_rev' => 'foobar')
+      @art['_rev'].should_not == 'foobar'
+    end
+    it "should silently ignore created_at" do
+      @art.update_attributes_without_saving('created_at' => 'foobar')
+      @art['created_at'].should_not == 'foobar'
+    end
+    it "should silently ignore updated_at" do
+      @art.update_attributes_without_saving('updated_at' => 'foobar')
+      @art['updated_at'].should_not == 'foobar'
+    end
     it "should also work using attributes= alias" do
       @art.respond_to?(:attributes=).should be_true
       @art.attributes = {'date' => Time.now, :title => "something else"}