no sprava sa to presne podla toho ako je to pre utf8_czech_ci collation specifikovane, vid:
http://collation-charts.org/mysql60/mysql604.utf8_ czech_ci.html
tvoj problem by vyriesilo ine collation, napr utf8_general_ci... ale to zase
moze robit problemy pri sortovani, ze znaky z diakritikov bude radit az nakoniec...