Index: wp-includes/pluggable.php
===================================================================
--- wp-includes/pluggable.php	(revision 22556)
+++ wp-includes/pluggable.php	(working copy)
@@ -1639,7 +1639,7 @@
 
 	if ( 'mystery' == $default )
 		$default = "$host/avatar/ad516503a11cd5ca435acc9bb6523536?s={$size}"; // ad516503a11cd5ca435acc9bb6523536 == md5('unknown@gravatar.com')
-	elseif ( 'blank' == $default )
+	elseif ( empty($email) && 'blank' == $default )
 		$default = includes_url('images/blank.gif');
 	elseif ( !empty($email) && 'gravatar_default' == $default )
 		$default = '';