Changes are in:
/libraries/joomla/html/html/select.php after line 125
/administrator/components/com_k2/models/extrafield.php in lines: 60, 298, 224
/administrator/components/com_k2/views/extrafield/view.html.php in line 47
/administrator/components/com_k2/views/extrafields/view.html.php in line 72
/media/k2/assets/js/k2.js in line 523
/components/com_k2/models/item.php in line 1035
/administrator/language/en-GB/en-BG.com_k2.ini in line 445
Unzip all files into root of your Joomla! and have fun ;)