in 2.7.1 in adminpanel - in items - doesnt works filter by title on Cyrillic simbols. Numbers and latin simbols works.
in
administrator\components\com_k2\models\items.php
line 39
was just:
$search = JString::strtolower($search);
now added the line:
$search = trim(preg_replace('/[^a-zA-Z0-9\s\-_]/', '', $search));