NetRange: 172.16.0.0 - 172.31.255.255
NetType: IANA Special Use
Comment: This block is reserved for special purposes.
Comment: Please see RFC 1918 for additional information.
This is what I saw in the whois.
It's not that they *should not* use that IP space for their public servers, it's that they *can not* use it. All ISPs filter IP traffic for that range (as well as 192.168.0.0/16 and 10.0.0.0/8) at their border routers (and most likely other places inside their networks as well), so traffic originating from or destined to those IPs are dropped as soon as they hit their upstream provider's routers. Are you sure that your client isn't behind a firewall or NAT that is translating those IPs to public IPs?