set_radio function

Hi, I'm Daniel, and I've been using Code Igniter for two months. I'm really thankful for the work on this framework.

I'm developing a little application and found a strange behavior in set_radio function, from the Form Helper. I would like to ask if this behavior is correct or it's a bug.
I have an update form. I have a list of links that represent people, so the user clicks a link and gets the form populated with person's data. With this way, passing parameters through GET method, everything works fine. All fields are populated correctly. 
Today I figure a security problem with this approach so I changed things a little. Instead of a list of links I created a form with options, using radio buttons, so the user selects an option and his choice is sent to the application through POST. Then, the form is displayed and populated with the respective data. With this approach, all fields are populated except the radio button fields.

With gratitude,
Daniel