This is a b2evolution blog. There’s a second blog running from the same installation, and the comment form was stalling on page load, displaying ‘Loading …’ and the icon, but never finishing.
The first action I took was to upgrade the blog. Many times, issues like that are resolved on an upgrade.
Unfortunately, that didn’t solve the problem.
Next, I reviewed the configuration of both blogs through the admin interface, taking care to clear the cache after each change.
Unfortunately this didn’t solve the problem either, so I grepped through the code until I found where the $baseurl is set. It is in these lines in conf/_basic_config.php. Uncommenting these lines solves the problem.