designerwest sent you a friend request so we could pm.
Thanks Jason.
In the meantime, if it helps anyone else, I have implemented javascript with jQuery to work around the issue.
The serverside code remains a relative link so the extension works. The images to modify need to be found by a selector (class, id, images within a specific container, or just all image tags if you are resizing all of them. The code checks the src of each of thos image tags and adds a / at the beginning if it is not already the first character.
$().ready(function() {
// Fix for non-site root relative links with WA Image Resize.
if ($(".postItemPic img").length) {
$(".postItemPic img").each(function() {
if ($(this).attr("src").indexOf("/") != 0) {
$(this).attr("src","/"+$(this).attr("src"));
}
});
}
});