This turns out to be a bug in the Plugin. Here’s how I fixed it:
On line 360 of sitemap-ui.php remove the action=”…” section from the <form> tag. It’s unneeded since the page will automatically submit to the same URL and the getBackLink() code is clearly giving it the wrong URL. Once I did that it worked fine, even hosted under a different path and redirected with .htaccess rules. This is the only plugin I have that was suffering from this.
It will now just read:
<form method=”post”>
Cheers,
Karl
