MySQL Workbench - producing bad SQL?

I'm trying to make a table that has a "created" timestamp and an "updated" timestamp (and have MySQL insert values in there automatically for me). It's doable, see: http://gusiev.com/2009/04/update-and-create-timestamps-with-mysql/.

As a first step, I copied the example table from the reference site and modeled it in Workbench. I then did a forward engineer and tested the resulting SQL in phpMyAdmin. Everything worked. Here was the SQL:

-- -----------------------------------------------------
-- Table `test_table`
-- -----------------------------------------------------

DROP TABLE IF EXISTS `test_table` ;

CREATE  TABLE IF NOT EXISTS `test_table` (
  `id` INT NOT NULL AUTO_INCREMENT ,
  `stamp_created` TIMESTAMP NULL DEFAULT '0000-00-00 00:00:00' ,
  `stamp_updated` TIMESTAMP NULL DEFAULT now() on update now() ,
  PRIMARY KEY (`id`) )
ENGINE = InnoDB;

After verifying that the idea works, I then implemented the concept in one of my actual tables. The resulting SQL was this:

-- -----------------------------------------------------
-- Table `user_login`
-- -----------------------------------------------------

DROP TABLE IF EXISTS `user_login` ;

CREATE  TABLE IF NOT EXISTS `user_login` (
  `user_login_id` INT NOT NULL AUTO_INCREMENT ,
  `user_id` INT NOT NULL ,
  `hashed_password` CHAR(255) NULL ,
  `provider_id` CHAR(255) NULL ,
  `provider_name` CHAR(255) NULL ,
  `unverified_email_address` CHAR(255) NULL ,
  `verification_code_email_address` CHAR(255) NULL ,
  `verification_code_password_change` CHAR(255) NULL ,
  `verified_email_address` CHAR(255) NULL ,
  `stamp_created` TIMESTAMP NULL DEFAULT '0000-00-00 00:00:00' ,
  `stamp_updated` TIMESTAMP NULL DEFAULT now() on update now() ,
  `stamp_deleted` TIMESTAMP NULL ,
  PRIMARY KEY (`user_login_id`) ,
  INDEX `user_login_user_id` (`user_id` ASC) ,
  UNIQUE INDEX `verified_email_address_UNIQUE` (`verified_email_address` ASC) ,
  UNIQUE INDEX `unverified_email_address_UNIQUE` (`unverified_email_address` ASC) ,
  CONSTRAINT `user_login_user_id`
    FOREIGN KEY (`user_id` )
    REFERENCES `user` (`user_id` )
    ON DELETE NO ACTION
    ON UPDATE NO ACTION)
ENGINE = InnoDB;

When I execute the SQL, I get the following error:

#1067 - Invalid default value for 'stamp_created'

Anyone see what's causing my problem?