diff --git a/activemodel/lib/active_model/observing.rb b/activemodel/lib/active_model/observing.rb
index eb853f01ee..c6a79acf81 100644
--- a/activemodel/lib/active_model/observing.rb
+++ b/activemodel/lib/active_model/observing.rb
@@ -1,6 +1,7 @@
 require 'singleton'
 require 'active_support/core_ext/array/wrap'
 require 'active_support/core_ext/module/aliasing'
+require 'active_support/core_ext/module/remove_method'
 require 'active_support/core_ext/string/inflections'
 
 module ActiveModel
@@ -157,7 +158,7 @@ module ActiveModel
       def observe(*models)
         models.flatten!
         models.collect! { |model| model.respond_to?(:to_sym) ? model.to_s.camelize.constantize : model }
-        remove_method(:observed_classes)
+        remove_possible_method(:observed_classes)
         define_method(:observed_classes) { models }
       end
 
diff --git a/activerecord/lib/active_record/persistence.rb b/activerecord/lib/active_record/persistence.rb
index 8d093c81de..828a8b41b6 100644
--- a/activerecord/lib/active_record/persistence.rb
+++ b/activerecord/lib/active_record/persistence.rb
@@ -106,15 +106,17 @@ module ActiveRecord
     # or callbacks. This is especially useful for boolean flags on existing records.
     def update_attribute(name, value)
       send("#{name}=", value)
-      primary_key = self.class.primary_key
-      h = {name => value}
-      if should_record_update_timestamps
-        self.send(:record_update_timestamps)
-        current_time = current_time_from_proper_timezone
-        timestamp_attributes_for_update_in_model.each { |column| h.merge!(column => current_time) }
+      hash = { name => read_attribute(name) }
+
+      if record_update_timestamps
+        timestamp_attributes_for_update_in_model.each do |column|
+          hash[column] = read_attribute(column)
+        end
       end
-      self.class.update_all(h, {primary_key => self[primary_key]}) == 1
+
       @changed_attributes.delete(name.to_s)
+      primary_key = self.class.primary_key
+      self.class.update_all(hash, { primary_key => self[primary_key] }) == 1
     end
 
     # Updates all the attributes from the passed-in Hash and saves the record. 
diff --git a/activerecord/lib/active_record/timestamp.rb b/activerecord/lib/active_record/timestamp.rb
index e6d52744df..1075a60f07 100644
--- a/activerecord/lib/active_record/timestamp.rb
+++ b/activerecord/lib/active_record/timestamp.rb
@@ -49,8 +49,8 @@ module ActiveRecord
         write_attribute('created_at', current_time) if respond_to?(:created_at) && created_at.nil?
         write_attribute('created_on', current_time) if respond_to?(:created_on) && created_on.nil?
 
-        timestamp_attributes_for_update.each do |column|
-          write_attribute(column.to_s, current_time) if respond_to?(column) && self.send(column).nil?
+        timestamp_attributes_for_update_in_model.each do |column|
+          write_attribute(column.to_s, current_time) if self.send(column).nil?
         end
       end
 
@@ -63,23 +63,17 @@ module ActiveRecord
     end
 
     def record_update_timestamps
-      if should_record_update_timestamps
+      if record_timestamps && (!partial_updates? || changed?)
         current_time = current_time_from_proper_timezone
         timestamp_attributes_for_update_in_model.each { |column| write_attribute(column.to_s, current_time) }
+        true
+      else
+        false
       end
     end
 
-    def should_record_update_timestamps
-      record_timestamps && (!partial_updates? || changed?)
-    end
-
-
-    def timestamp_attributes_for_update #:nodoc:
-      [:updated_at, :updated_on]
-    end
-
     def timestamp_attributes_for_update_in_model #:nodoc:
-      ([:updated_at, :updated_on].inject([]) { |sum, elem| respond_to?(elem) ? sum << elem : sum })
+      [:updated_at, :updated_on].select { |elem| respond_to?(elem) }
     end
     
     def current_time_from_proper_timezone #:nodoc: