It is possible to break the AJAX drag and drop functionality within a section using two combinations of HTML lists

The first is an order list with a nested unordered list followed by a seperate ordered list

The second is an unordered list with a nexted ordered list followed by a sepearte unordered list.

In both cases drag and drop for the elements within the section that the summary is in does not activate. (however if an element from another section is dragged in it does not loose drag and drop functionality until the page is refreshed)

The two miniumum html examples are:

<ul>
<li>test</li>
<ol>
<li>test</li>
</ol></ul>
<ul>
<li>test</li>
</ul>

and

<ol>
<li>test</li>
<ul>
<li>test</li>
</ul></ol>
<ol>
<li>test</li>
</ol>

Just found it to be happening in Moodle 2.3 as well as the 2.1.x versions I found it on