The insert script could not be added into the document and the modal popup can not be closed by selecting (Insert) a file, you can have a little hacking into the t3 core as following
Open the file pluginssystemjat3jat3coreadminutil.php, at about line number 640 you would see a line of code like this
JHTML::_ ( ‘behavior.modal’ );
just add below it this code
$script = array();
$script[] = ' function jInsertFieldValue(value, id) {';
$script[] = ' var old_id = document.id(id).value;';
$script[] = ' if (old_id != id) {';
$script[] = ' var elem = document.id(id)';
$script[] = ' elem.value = value;';
$script[] = ' elem.fireEvent("change");';
$script[] = ' }';
$script[] = ' }';
$dc = &JFactory::getDocument();
// Add the script to the document head.
$dc->addScriptDeclaration(implode("n", $script));
Hope that help !