I believe I actually noticed this in an earlier version and fixed it myself.
Looking at wp-includes/template-functions-category.php, the problem atleast for me is found at line 352, assuming youve made no other changes.
it reads:
if ( !empty($feed_image) )
$link .= "<img src='$feed_image' $alt$title" . ' />';
Now my current php is substantially different elsewhere as well, but this is what I did:
if (! empty($feed_image)) {
$link .= "<img src="$feed_image" class="feedimage" border="0" alt="RSS Feed"...;
that alone wont work for you, you will need to close that tag obviously...
if (! empty($feed_image)) {
$link .= "<img src="$feed_image" class="feedimage" border="0" alt="RSS Feed" .... <-- close this
But you get the idea, im sure :)
oh and btw, all of my quotes are escaped, the forum removed them for some reason. ..