diff -Nur redmine-1.1.0/app/controllers/issues_controller.rb redmine-1.1.0-rollback/app/controllers/issues_controller.rb
--- redmine-1.1.0/app/controllers/issues_controller.rb	2011-01-09 17:05:00.000000000 -0700
+++ redmine-1.1.0-rollback/app/controllers/issues_controller.rb	2011-02-11 10:54:47.912319200 -0700
@@ -19,7 +19,7 @@
   menu_item :new_issue, :only => [:new, :create]
   default_search_scope :issues
   
-  before_filter :find_issue, :only => [:show, :edit, :update]
+  before_filter :find_issue, :only => [:show, :edit, :update, :rollback]
   before_filter :find_issues, :only => [:bulk_edit, :bulk_update, :move, :perform_move, :destroy]
   before_filter :check_project_uniqueness, :only => [:move, :perform_move]
   before_filter :find_project, :only => [:new, :create]
@@ -27,7 +27,7 @@
   before_filter :find_optional_project, :only => [:index]
   before_filter :check_for_default_issue_status, :only => [:new, :create]
   before_filter :build_new_issue_from_params, :only => [:new, :create]
-  accept_key_auth :index, :show, :create, :update, :destroy
+  accept_key_auth :index, :show, :create, :update, :destroy, :rollback
 
   rescue_from Query::StatementInvalid, :with => :query_statement_invalid
   
@@ -56,10 +56,11 @@
   verify :method => [:post, :delete],
          :only => :destroy,
          :render => { :nothing => true, :status => :method_not_allowed }
-
+         
   verify :method => :post, :only => :create, :render => {:nothing => true, :status => :method_not_allowed }
   verify :method => :post, :only => :bulk_update, :render => {:nothing => true, :status => :method_not_allowed }
   verify :method => :put, :only => :update, :render => {:nothing => true, :status => :method_not_allowed }
+  verify :method => :post, :only => :rollback, :render => { :nothing => true, :status => :method_not_allowed }
   
   def index
     retrieve_query
@@ -214,6 +215,21 @@
     redirect_back_or_default({:controller => 'issues', :action => 'index', :project_id => @project})
   end
   
+  def rollback
+    if @issue.rollback
+      flash[:notice] = l(:notice_successful_update)
+    else
+      # can't seem to bring in the helper method 'error_messages_for'
+      # and injecting it into show.rhtml doesn't seem to work, since 
+      # the @issue loses the errors on redirect (due to issue reload)
+      flash[:error] = "<ul>" + @issue.errors.full_messages.map {|msg| "<li>" + ERB::Util.html_escape(msg) + "</li>"}.join + "</ul>"
+    end
+    respond_to do |format|
+      format.html { redirect_back_or_default({:action => 'show', :id => @issue}) }
+      format.api  { render_validation_errors(@issue) }
+    end
+  end
+  
   def destroy
     @hours = TimeEntry.sum(:hours, :conditions => ['issue_id IN (?)', @issues]).to_f
     if @hours > 0
diff -Nur redmine-1.1.0/app/models/issue.rb redmine-1.1.0-rollback/app/models/issue.rb
--- redmine-1.1.0/app/models/issue.rb	2011-01-25 13:02:02.750334900 -0700
+++ redmine-1.1.0-rollback/app/models/issue.rb	2011-02-11 10:54:47.927944400 -0700
@@ -358,6 +358,32 @@
     @current_journal
   end
   
+  # rolls back the last journal entry
+  def rollback
+    journal = journals.find(:last, :include => [:details], :order => "#{Journal.table_name}.created_on ASC")
+    transaction do
+      old_parent = nil
+      journal.details.each do |d|
+        if d.property == 'attr'
+          if d.prop_key == 'parent_id'
+            @parent_issue = Issue.find_by_id(d.old_value)
+          else
+            send("#{d.prop_key}=", d.old_value)
+          end
+        elsif d.property == 'cf'
+          custom_field_values.each {|v| v.value = d.old_value if v.custom_field_id == d.prop_key.to_i}
+        elsif d.property == 'attachment'
+          if d.old_value == nil
+            @rolling_back = true # avoid journal entries created in 'attachment_removed'
+            attachments.each {|v| attachments.delete(v) if v.id == d.prop_key.to_i}
+            remove_instance_variable(:@rolling_back)
+          end
+        end
+      end
+      journal.destroy if save(false)
+    end
+  end
+  
   # Return true if the issue is closed, otherwise false
   def closed?
     self.status.is_closed?
@@ -785,11 +811,13 @@
   
   # Callback on attachment deletion
   def attachment_removed(obj)
-    journal = init_journal(User.current)
-    journal.details << JournalDetail.new(:property => 'attachment',
-                                         :prop_key => obj.id,
-                                         :old_value => obj.filename)
-    journal.save
+    if !@rolling_back
+      journal = init_journal(User.current)
+      journal.details << JournalDetail.new(:property => 'attachment',
+                                           :prop_key => obj.id,
+                                           :old_value => obj.filename)
+      journal.save
+    end
   end
   
   # Default assignment based on category
@@ -850,7 +878,7 @@
       init_journal @current_journal.user, @current_journal.notes
     end
   end
-
+  
   # Query generator for selecting groups of issue counts for a project
   # based on specific criteria
   #
diff -Nur redmine-1.1.0/app/views/issues/_history.rhtml redmine-1.1.0-rollback/app/views/issues/_history.rhtml
--- redmine-1.1.0/app/views/issues/_history.rhtml	2011-01-09 17:05:00.000000000 -0700
+++ redmine-1.1.0-rollback/app/views/issues/_history.rhtml	2011-02-11 10:54:47.943569600 -0700
@@ -2,6 +2,9 @@
 <% for journal in journals %>
   <div id="change-<%= journal.id %>" class="<%= journal.css_classes %>">
     <h4><div class="journal-link"><%= link_to "##{journal.indice}", :anchor => "note-#{journal.indice}" %></div>
+    <% if journal == journals.last && authorize_for('issues', 'rollback') %>
+      <div class="journal-rollback"><%= link_to_if_authorized(image_tag('cancel.png'), {:controller => 'issues', :action => 'rollback', :id => @issue}, :confirm => l(:text_are_you_sure), :method => :post, :title => l(:label_rollback)) %>&nbsp;</div>
+    <% end %>
     <%= avatar(journal.user, :size => "24") %>
     <%= content_tag('a', '', :name => "note-#{journal.indice}")%>
 		<%= authoring journal.created_on, journal.user, :label => :label_updated_time_by %></h4>
diff -Nur redmine-1.1.0/config/locales/en.yml redmine-1.1.0-rollback/config/locales/en.yml
--- redmine-1.1.0/config/locales/en.yml	2011-01-09 17:05:00.000000000 -0700
+++ redmine-1.1.0-rollback/config/locales/en.yml	2011-02-11 10:57:04.132812800 -0700
@@ -378,6 +378,7 @@
   permission_add_issue_notes: Add notes
   permission_edit_issue_notes: Edit notes
   permission_edit_own_issue_notes: Edit own notes
+  permission_rollback_issues: Rollback issues
   permission_move_issues: Move issues
   permission_delete_issues: Delete issues
   permission_manage_public_queries: Manage public queries
@@ -793,6 +794,7 @@
   label_project_copy_notifications: Send email notifications during the project copy
   label_principal_search: "Search for user or group:"
   label_user_search: "Search for user:"
+  label_rollback: Rollback
   
   button_login: Login
   button_submit: Submit
diff -Nur redmine-1.1.0/lib/redmine.rb redmine-1.1.0-rollback/lib/redmine.rb
--- redmine-1.1.0/lib/redmine.rb	2011-01-09 17:05:00.000000000 -0700
+++ redmine-1.1.0-rollback/lib/redmine.rb	2011-02-11 10:56:01.350759200 -0700
@@ -72,6 +72,7 @@
     map.permission :add_issue_notes, {:issues => [:edit, :update], :journals => [:new]}
     map.permission :edit_issue_notes, {:journals => :edit}, :require => :loggedin
     map.permission :edit_own_issue_notes, {:journals => :edit}, :require => :loggedin
+    map.permission :rollback_issues, {:issues => [:rollback]}
     map.permission :move_issues, {:issue_moves => [:new, :create]}, :require => :loggedin
     map.permission :delete_issues, {:issues => :destroy}, :require => :member
     # Queries
diff -Nur redmine-1.1.0/public/stylesheets/application.css redmine-1.1.0-rollback/public/stylesheets/application.css
--- redmine-1.1.0/public/stylesheets/application.css	2011-01-09 17:05:00.000000000 -0700
+++ redmine-1.1.0-rollback/public/stylesheets/application.css	2011-02-11 10:54:47.990445200 -0700
@@ -938,6 +938,10 @@
 	float: right;
 }
 
+.journal-rollback {
+	float: right;
+}
+
 h2 img { vertical-align:middle; }
 
 .hascontextmenu { cursor: context-menu; }