Dropdown and Converter

I have a dropdown with an option group inside. The control value of the dropdown is a field in my bean and the converter value is a custom converter. The problem is the converter is called with the option value instead of the control value. Here my example: I have 3 dropdown, one for year, one for month and one for day. The 3 dropdown have the same control value that point in the field date in my bean (String yyyymmdd).