Two captchas on one page

I have two captchas on one page. One for the Member login and another for Guest login form.

public function actions()
{
    return array(
	'captcha1'=>array(
		'class'=>'CCaptchaAction',
		'backColor'=>0xFFFFFF,
	),

	'captcha2'=>array(
		'class'=>'CCaptchaAction',
		'backColor'=>0xFFFFFF,
	),


	'page'=>array(
		'class'=>'CViewAction',
	),
    );
}

However, only one of the key is generated in the yii session table:

Yii.CCaptchaAction.3bbe352e.controllername.captcha|s:7:"xemobin"

I am expecting both:

Yii.CCaptchaAction.3bbe352e.controllername.captcha|s:7:"xemobin"
Yii.CCaptchaAction.3bbe352e.controllername.captcha2|s:8:"derbdgha"


However, both keys will generate after first failed attempt.

Do you know why is this the case?

Thank you,
MISC