UTF-8 does not work

[applibs]

When I use rule alpha_space with string like this "ěščřžýáí" validation resilt is false.
After I changed this line:
return preg_match('/^(['.self::$alpha_regex.'\s])+$/i', $value) > 0;
into:
return preg_match('/^(['.self::$alpha_regex.'\s])+$/ui', $value) > 0;

then it works as expected.