Btw, here is a mbstring based PHP implementation that should do the job correctly:

    function grapheme_stripos($s, $needle, $offset = 0)
    {
        if ($offset < 0) $offset = 0;
        if (!$needle = mb_stripos($s, $needle, $offset, 'UTF-8')) return $needle;
        return grapheme_strlen(mb_substr($s, 0, $needle, 'UTF-8'));
    }

    function grapheme_strripos($s, $needle, $offset = 0)
    {
        if ($offset < 0) $offset = 0;
        if (!$needle = mb_strripos($s, $needle, $offset, 'UTF-8')) return $needle;
        return grapheme_strlen(mb_substr($s, 0, $needle, 'UTF-8'));
    }

Could you please check the attached pull request and see if it fixes your issues?

It seems ok.

Besides, it should work, if we consider UTS #10:

Ideally, the UCA at a secondary level would be compatible with the standard Unicode case folding and removal of compatibility differences, especially for the purpose of matching. For the vast majority of characters, it is compatible, but there are few exceptions.

Thanks.