Problem after fadeIn an input value

SO here’s my problem, which I cannot understand why it happens.

I have a form for a user registration and in some point I have the security question options. If the user selects “Write my own question”, I use jquery and fadeIn a textbox where he can write his own question. The problem is that in this case when the user submits the registration form, this “custom” question is not posted in the $_POST[‘RegisterForm’] array, but I have to explicitly retrieve it by using $_POST[“RegisterForm”][“custom_security_question”]…

Does anybody know what that happens? is there any solution? thanx!

I had not put the attribute in the ‘safe’ attributes…so the value was actually posted but could not be assigned to the form model attribute