Hello,
In 0.2.1 You must alter 2 files :
program/include/rcube_template.php :
$input_user = new html_inputfield(array('name' => '_user', 'id' => 'rcmloginuser', 'size' => 30, 'autocomplete' => 'off'));
to
$input_user = new html_inputfield(array('name' => '_user', 'id' => 'rcmloginuser', 'size' => 30, 'autocomplete' => 'on'));
and :
program/js/app.js :
obj.setAttribute('autocomplete', 'off');
to
obj.setAttribute('autocomplete', 'on');
That was worked for me