Undefined index: user_pwd

I'm getting this error in my logs and don't know why?

PHP Notice: Undefined index: user_pwd in /srv/www/htdocs/forum/bb_func_login.php on line 13, referer:

Line 13 in bb_func_login.php looks like this:
$user_pwd=htmlspecialchars(trim($_POST['user_pwd']),ENT_QUOTES);

Is that because this users password has special chars and its not trimming them correctly?

This bug has been fixed in miniBB 2.0.5a.

Please upgrade your version or use bb_func_login.php from the latest release.

Thanks for the reporting anyway.