Point of origin:
You changed the reverse entry of your server IP via the customer center.
If you conduct a Traceroute to your server the "old" reverse entry is still being showed.
This is not a problem. It's caused by the so called "DNS caching" where every provider caches DNS requests for a certain time in order to relieve his DNS servers. When this time has expired the DNS cache is being refreshed and the right reverse entry for the IP showed.