The principle of the Domain Name System (DNS) is that it decouples the name of a web domain (eg looselycoupled.com) from the IP address of the physical server where it resides (eg 184.108.40.206). But when a site is hosted on a shared server, it's often impossible for the site owner to benefit from this separation even if the hosting provider is one of the few that allocate a unique, fixed IP address to each of their shared-server customers.
Most web hosting companies offer DNS hosting as a package with server hosting, and in the process they tightly couple the two together. When you open a typical shared-server account, one of the first things you will be asked is the name of the domain. Even if you already host the DNS somewhere else, the provider will still enter that domain name on their own systems.
This is fine if you host the entire site with that provider. But it isn't if, like Loosely Coupled, you host part of the site elsewhere, and want the two servers to be able to read each others' pages. Your providers will each set up their internal DNS as if they host the entire site, with the result that your servers will never find each other, because they'll never look out on the Internet for other hostnames in the domain.
In the case of Hostcentric, which currently hosts howto.looselycoupled.com, the only solution was to pay a fee in order to change the account to a different domain name (leaving the problem intact for that other domain name, but at least solving it for this site). Fortunately, the people at Jumpline, whose server hosts both www.looselycoupled.com and news.looselycoupled.com, have been more helpful. Without making a charge, their helpdesk simply blanked the references to the domain name from their servers once the problem had been explained to them.
I'm pleased to have spotted the problem and to have had it fixed, but I'm still perturbed that it exists at all. I find it bizarre that providers who explicitly offer fixed IP addresses as part of their shared-server packages nevertheless appear to be blindsided when customers take advantage of that capability to host their site across multiple providers. I know there are other reasons for preferring fixed IP (apparently it helps your Google ranking, for one thing). But it seems odd that separately hosted DNS is such a rarity.
Instead of having to carefully explain myself every time, I would much rather find a hosting provider that takes this in its stride. It wouldn't take much to put a checkbox in the administrator console that lets a customer say "I host my DNS at a third party." It would leave everyone knowing exactly where they stand, and remove this lingering fear I have that someone is going to forget one day and change the DNS setup back again. Surely this is an opening in the market that someone ought to step into.