Darnit, this is the third time I've posted this. WHy have my previous two posts just gone missing!
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Thanks for the reply.
But something has gone wrong with the forum post. I had posted right after, and discovered what the issue is, but that post is missing here now. I'll try to recreate my post from memory:
Here are the results w/blacklisting disabled:
https://dl.dropboxusercontent.com/u/87189402/macys-citibank-good.png
We see that iesnare.com is present in this output.
Given iesnare's reputation and purpose, I suppose that is the issue. With blacklisting re-enabled:
$ host iesnare.com
iesnare.com has address 0.0.0.0
So certainly this is one, if not the, cause of the issue.