Submit Button Disabled After Webform Validation Error(s) Corrected

My webform has a variety of webform components (text fields, checkboxes and drop down menus) on it. A few of the text fields are mandatory/required. The webform works perfectly as long as the user fills in all of the required fields on their first try. If they miss a required field, validation seemingly disables the submit button even after the user completes the mandatory fields.

Aside from disabling the submit button, validation works correctly if a user does not fill in one or more of the mandatory fields. The field(s) are highlighted in red and messages appear prompting the user to fill the fields out. It appears that the problem is specific to the submit button.

The AJAX loading graphic appears briefly and then disappears when a user clicks on the submit button after correcting validation errors, but the form never submits.

The form has additional submit actions attached to it in a custom module. The form also uses the CAPTCHA module.

The additional custom module for the form contains the following code:

function mytheme_form_alter(&$form, &$form_state,$form_id){
  if($form_id == 'webform_client_form_60983') {
	array_unshift($form['#submit'], 'media_kit_node_form_submit');	  	  
  }
}

function media_kit_node_form_submit($form, &$form_state) {

/* A lot of code looking at $form_state['values']['submitted'], doing mysql queries, creating email messages and providing the user with a confirmation message. */

}

Has anyone else experienced this and if so, is there a fix? Is there something that may be missing from my custom submit function? Any help is very much appreciated.