Plugin throwing error on quote revise

Hello we have a small plugin that brings over some extra variables from the product entity to the quotedetails entity and everything works great except for when you go to revise a quote that is already activated then it throws an "An item with the same key has already been added." error, disable the plugin and the error goes away.  Does revising a quote create some odd state in the system? I'm not sure why it's re-firing the on create method for quotedetail

The fields follow similar syntax to below

//copy values
                            if (ProdTemp.Contains("description") == false)
                            {
                                if (entity.Contains("description") == true)
                                    entity.Attributes["description"] = "Description Missing";
                                else
                                    entity.Attributes.Add("description", "Description Missing");
                            }
                            else
                            {
                                if (entity.Contains("descirption") == true)
                                    entity.Attributes["description"] = ProdTemp.Attributes["description"].ToString();
                                else
                                    entity.Attributes.Add("description", ProdTemp.Attributes["description"].ToString());
                            }

any suggestions?

Thank you.