PTR records are a special case. Whoever supplies your IP addresses (usually your host/ISP), must do one of the following:
- Set up your reverse DNS entries on their DNS servers.
- Delegate authority" for your reverse DNS entries to your DNS servers.
This has to do with the unique nature in which reverse DNS is resolved.
I would contact your host to resolve this and disable/remove the PTR records on the Plesk system.
Another note about reverse DNS is that it is a 1:1 mapping. You should not have multiple PTR records mapping an IP to a domain. In contrast, you can have multiple A records mapping different domains to the same IP.
Here is a good resource on PTRs.