I think 2 are different places. one output for shortcode and another output for main message page. For shortcode it is already filled with page title but main message page that is not happening. You can only hide shortcode message title and not main page message title using following code instead of #message_title{display:none;}
.fep-form-shortcode-newmessage .fep-form-field-message_title{display:none;} (works in version 6.4 or later)