String.h function lastIndexOf return value is not correct

[hunteras]

size_t lastIndexOf(char ch, size_t from = npos, CaseSensitivity cs = CaseSensitive) const
{
    if (cs == CaseSensitive)
        return mString.rfind(ch, from == npos ? std::string::npos : size_t(from));
    const char *data = mString.c_str();
    if (from == npos)
        from = mString.size() - 1;
    ch = tolower(ch);
    int f = static_cast<int>(from);
    while (f >= 0) {
        if (tolower(data[f]) == ch)
            return **from**;
        --f;
    }
    return npos;
}

this function should return f instead of from, from is always size() - 1.