There is a bug in utf8_encode in utf8.c

[crazyyao0]

    out[1] = 0x80 + (((c >> 8) & 0x1f) << 2) + ((c >> 6) & 0x3);

should be
out[1] = 0x80 + (((c >> 8) & 0xf) << 2) + ((c >> 6) & 0x3);