If you try to post url with non-latin symbols (example:
https://ru.wikipedia.org/wiki/Миллиган,_Билли ) you get an error.
Solution:

file: /includes/functions_content.php
function: make_clickable_callback
string:
$short_url = (strlen($url) > 55) ? substr($url, 0, 39) . ' ... ' . substr($url, -10) : $url;

replace with multi-byte versions:
$short_url = (mb_strlen($url) > 55) ? mb_substr($url, 0, 39) . ' ... ' . mb_substr($url, -10) : $url;