This seems to be a bug, because "linode.com" is not on the public suffix list. Several subdomains and related domains are, but not linode.com:
// Linode : https://linode.com
// Submitted by security@linode.com
members.linode.com
*.nodebalancer.linode.com
*.linodeobjects.com
ip.linodeusercontent.com
I would expect get_public_suffix("ns1.linode.com") to return "linode.com"