Validate custom textbox, text not updated with client side validation

Hi Guys,
I've build a custom control which implement the TextBox class. The custom control builds a ckEditor WYSIWYG. Within this control I also build a Reguired Field Validator.
Everything works fine, except for one little thing.
 
When I submit the form with this custom control via a button , I must click twice on the button before the Required Field Validator validates the input correctly. I think it is always one step behind with updating the text property of the custom control client side.
When I delete the following lines (but then the editor is not rendered), the validator works fine (this code exists within the Render method of the control)
Editor += string.Format("<textarea name=\"{0}\" type=\"text\" id=\"{1}\"></textarea>", UniqueID, ClientID); Editor += string.Format("<script type='text/javascript' ...