Two changes in sources/admin/ManageAttachments.controller.php:
elseif ($file != 'index.php')
elseif ($file != 'index.php' && !is_dir($attach_dir . '/' . $file))
Then, just after:
$context['completed'] = $fix_errors ? true : false;
add:
$context['errors_found'] = false;
ETA: I'm not 100% sure this will fix your issue, though it fixed mine... lol