thanks. So I used a browser switch in qa-wysiwyg-editor.php:
// detect IE for workaround flickering, inserts pseudo element
if( strpos($_SERVER['HTTP_USER_AGENT'], 'MSIE') ) {
$qa_content['script_lines'][]=array(
"qa_wysiwyg_editor_config={toolbar:[".
// first element is pseudo element for flickering bug of IE
"['-'],".
"['Image'],".
...
it works.