You may see DNS records being added with the domain appearing twice. For example, when adding the subdomain subdomain.example.com, the record is added as subdomain.example.com.example.com.
This can occur if a full domain or subdomain is provided but it does not end with a "." (period) character. The domain will be appended to any name entry that does not end in a "." character.
When adding a record, either the full name should be provided with a "." at the end, or only the portion proceeding the domain should be used. For example, the following would be valid ways to add a subdomain record.