Activity details now appear twice when html contains <div> tags

Issue 18270 (https://issues.civicrm.org/jira/browse/CRM-18270) resolved the problem of html not being displayed properly in activity details.

However, it does seem to have introduced a regression, in that when an activity is viewed, if the html contains <div> tags, then the whole Details text is shown twice.

For example, if this html is the Activity Details:

<div style="color:#0000FF">

<h3>This is a heading</h3>

<p>This is a paragraph.</p>

</div>

then this is what is shown when the activity is viewed:

This is a heading
This is a paragraph.

This is a heading
This is a paragraph.

" id="details" />

This is easily demonstrable in the demo site.