as the word is broken at the end, this problem is very likely. you can use the following snippet instead which will finish at word boundary

    function short_title($after = '', $length)
    {
      $mytitle = get_the_title();
      if (strlen($mytitle) > $length) {
        $mytitle = substr($mytitle, 0, $length);
        $i = strrpos($mytitle, " ");
        $mytitle = substr($mytitle, 0, $i);
        echo $mytitle . $after;
      } else {
        echo $mytitle;
      }
    }
    
    short_title( '...', 40 );
ref: http://code.web-max.ca/truncate_string.php

however, if you have multibyte support, probably it's better idea to use mb_strlen() rather than strlen() function.