it's either on the blacklist because it's hosting a domain for 3rd party cookies or hosting advertisements. You've got to remember that from the perspective of these corpos, they're not actually doing anything nefarious, and they can host multiple vhosts from the same IP. Now, I haven't looked into it it's being blocked by an IP blacklist at the firewall, or a DNS advertisement blacklist.
But in short, I disagree. It is how that works.
Let's assume for the sake of argument that you're right. The IP has never been used for anything nefarious, and it's not being actively blacklisted. Oh my word! It suddenly started working! You fixed it :) thank you.