Ordem correta

app/models/course.rb

@@ -40,6 +40,9 @@ class Course < ActiveRecord::Base
 	has_many :wiki_pages,
 	         :order => "position",
 	         :dependent => :destroy
+
+	has_and_belongs_to_many :users,
+	         :order => "last_seen desc"
 	
 	# Validacao
 	generate_validations

app/models/log_entry/wiki_log_entry.rb

@@ -30,7 +30,7 @@ class WikiDeleteLogEntry < WikiLogEntry
 	end
 	def undo!(current_user)
 		wiki_page.update_attribute(:deleted_at, nil)
-		wiki_page.update_attribute(:position, wiki_page.course.wiki_pages.maximum(:position) + 1)
+		wiki_page.update_attribute(:position, (wiki_page.course.wiki_pages.maximum(:position)||0) + 1)
 		WikiRestoreLogEntry.create!(:target_id => wiki_page.id, :user_id => current_user.id, :course => wiki_page.course)
 	end
 end