Trackable URL option clobbers img src in mailing header.

The "trackable URL" option causes image src attributes in the HTML message to be inappropriately converted to trackable URLs.

My header contains images sourced from http://www.preventionaction.org/

<table border="0">
<tr style="height:80px;">
<td style="text-align:right;padding-right:1em;" bgcolor="#FFFFFF" valign="bottom" width="300">
<img src="http://www.preventionaction.org/sites/default/themes/prevenir/images/prevention.png" alt="Prevention" style="margin-left:8px;">
</td>
<td style="padding-left:1em;" bgcolor="#CC0001" valign="bottom" width="100%">
<img src="http://www.preventionaction.org/sites/default/themes/prevenir/images/action.png" alt="Action">
</td>
</tr>
</table>

The mailing is also announcing the web site at http://www.preventionaction.org, so it contains a link to the site.

The output of the header in the mail shows that the src for the first image is being converted to a trackable link. Oddly enough the second image is ignored and not converted to a trackable URL.

This means I have to choose between images in my HTML mail headers or trackable links.