Maintenance page being rendered as an entire page load after the main page load I've noticed that I've got a maintenance page being rendered in its entire HTML markup format after my pages. The site is not in maintenance mode, and this is not intentional behaviour. I'm trying to debug, but even as a reasonably experienced Drupal developer I still don't understand all the mechanisms at work here. Guidance on that would be welcomed.

I had been using the module CDN, to experiment with integrating a CDN. That was using that area at the bottom of the page, but when I disabled it, and uninstalled it, it has not stopped the problem.

I then enabled Theme developer 7.x-1.x-dev just to help me see what was going on, and the maintenance page render has stopped appearing. I then disabled Theme developer again and it has returned. Does this help anyone to suggest something?

&lt;/body&gt;
&lt;/html&gt;
&lt;!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
  "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"&gt;
&lt;html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en" dir="ltr"&gt;

&lt;head&gt;

[...]

&lt;/head&gt;
&lt;body class="maintenance-page in-maintenance no-sidebars"&gt;
  &lt;div id="page"&gt;
    &lt;div id="header"&gt;


This also displays on my admin theme. Does this mean it is not something to do with my custom theme? Is there anything in particular that I could look or has anyone seen this behaviour before?
I'm still waiting to see an answer to the question of what causes maintenance mode to be displaying messages. So I don't know specifically whether the recoverable fatal error (this issue) being thrown by the buggy 7.x-2.4 version of XML Sitemap module was what caused the avoidance of a general WSOD/ crash and yet a display of an odd maintenance mode message. 

I had not noticed they'd released 7.x-2.5 and so I've updated that which has stopped the behaviour altogether. Happy days :)