Why does VKontakte authorization fail if the password contains Cyrillic?

Question

Python

url = 'https://vk.com/'

session = requests.session()

data = session.get(url, headers=headers, proxies=random_proxy(good_http_proxy))

page = lxml.html.fromstring(data.content)

form = page.forms[0]
form.fields['email'] = login
form.fields['pass'] = "одиндва"

response1 = session.post(form.action, data=form.form_values(), proxies=random_proxy(good_http_proxy))
print(response1.text)

The answer comes:

<script type="text/javascript">
var _ua = navigator.userAgent;
var locDomain = 'vk.com'.match(/[a-zA-Z]+\.[a-zA-Z]+\.?$/)[0];
if (/opera/i.test(_ua) || !/msie 6/i.test(_ua) || document.domain != locDomain) {
  document.domain = locDomain;
}
parent.__qlClear();
addEvent = parent.addEvent;
vk = parent.vk;
parent.stManager.add(['notifier.js', 'notifier.css'], function() {
  Notifier = parent.Notifier;
  
  parent.onLoginFailed(4, {"email":"79104156591"});
});

If the password is written in Latin, then authorization is successful.