Dynamic content and 404 page

In case anyone is facing the same issue, until there is some official fix, you could
1.) change dynamic-cache-test.php line 104 to:

function dynamic_cache_test_template_tag() {
	echo "<!-- ".DYNAMIC_CACHE_TEST_TAG." -->"; // This is the template tag
}

so that the TEST_TAG doesn’t appear at the footer of the page, and

2.) add a display:none element around the DYNAMIC_OUTPUT_BUFFER_TAG that you put somewhere on your site, such as:

<?php if(function_exists('dynamic_output_buffer_test')) dynamic_output_buffer_test(); ?>
<pre style="display:none;">sqHAYayMpXvXvzrPLcHXSRRMLjXfmn</pre>