This morning, I received an email from Atom notifying me the nameservers for one of my domain names was not correctly set up. I remembered to change the nameservers when I added it to Atom, so I was confused by the email. I visited the domain name, and as Atom told me, the domain name resolved to its Afternic listing rather than its correct Atom listing.
A visit to my Namecheap control panel showed me what happened. While I had correctly changed NS1.Afternic / NS2.Afternic to the required Atom nameservers, I inadvertently left the Afternic verification nameserver resolving instead of deleting it. This caused the domain name to occasionally resolve to the previous landing page instead of the new one.