number of characters in Mysql

Question

Someone said that the TEXT type allows 65535 bytes, but I can’t post more than 10,000 characters, which I’m doing wrong?

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This is my Table

DROP TABLE IF EXISTS `cad_materia`;
CREATE TABLE IF NOT EXISTS `cad_materia` (
  `php_id` int(11) NOT NULL AUTO_INCREMENT,
  `php_titulo` text CHARACTER SET utf8 COLLATE utf8_unicode_ci NOT NULL,
  `php_thumb` text CHARACTER SET latin1 NOT NULL,
  `php_texto` longtext NOT NULL,
  `php_categoria` text CHARACTER SET latin1 NOT NULL,
  `php_autor` text CHARACTER SET latin1 NOT NULL,
  `php_data` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
  `php_chave` text CHARACTER SET latin1 NOT NULL,
  `url` text CHARACTER SET utf8 COLLATE utf8_unicode_ci NOT NULL,
  `cod_user` char(255) CHARACTER SET latin1 NOT NULL,
  PRIMARY KEY (`php_id`)
) ENGINE=MyISAM AUTO_INCREMENT=18 DEFAULT CHARSET=utf8;

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Well I am a beginner, in the text I did not put any value, the error gives when I will post the text co site,