Index: wp-includes/query.php
===================================================================
--- wp-includes/query.php	(revision 6563)
+++ wp-includes/query.php	(working copy)
@@ -60,11 +60,13 @@
 
 	$author_obj = $wp_query->get_queried_object();
 
-	if ( $author == $author_obj->ID )
+	$author = (array) $author;
+
+	if ( in_array( $author_obj->ID, $author ) )
 		return true;
-	elseif ( $author == $author_obj->nickname )
+	elseif ( in_array( $author_obj->nickname, $author ) )
 		return true;
-	elseif ( $author == $author_obj->user_nicename )
+	elseif ( in_array( $author_obj->user_nicename, $author ) )
 		return true;
 
 	return false;
@@ -81,11 +83,13 @@
 
 	$cat_obj = $wp_query->get_queried_object();
 
-	if ( $category == $cat_obj->term_id )
+	$category = (array) $category;
+
+	if ( in_array( $cat_obj->term_id, $category ) )
 		return true;
-	else if ( $category == $cat_obj->name )
+	elseif ( in_array( $cat_obj->name, $category ) )
 		return true;
-	elseif ( $category == $cat_obj->slug )
+	elseif ( in_array( $cat_obj->slug, $category ) )
 		return true;
 
 	return false;
@@ -93,6 +97,7 @@
 
 function is_tag( $slug = '' ) {
 	global $wp_query;
+
 	if ( !$wp_query->is_tag )
 		return false;
 
@@ -100,8 +105,12 @@
 		return true;
 
 	$tag_obj = $wp_query->get_queried_object();
-	if ( $slug == $tag_obj->slug )
+
+	$slug = (array) $slug;
+
+	if ( in_array( $tag_obj->slug, $slug ) )
 		return true;
+
 	return false;
 }
 
@@ -153,12 +162,12 @@
 	$page_obj = $wp_query->get_queried_object();
 
 	$page = (array) $page;
-    
-    if ( in_array( $page_obj->ID, $page ) )
+
+	if ( in_array( $page_obj->ID, $page ) )
 		return true;
 	elseif ( in_array( $page_obj->post_title, $page ) )
 		return true;
-	else if ( in_array( $page_obj->post_name, $page ) )
+	elseif ( in_array( $page_obj->post_name, $page ) )
 		return true;
 
 	return false;
@@ -208,11 +217,13 @@
 
 	$post_obj = $wp_query->get_queried_object();
 
-	if ( $post == $post_obj->ID )
+	$post = (array) $post;
+
+	if ( in_array( $post_obj->ID, $post ) )
 		return true;
-	elseif ( $post == $post_obj->post_title )
+	elseif ( in_array( $post_obj->post_title, $post ) )
 		return true;
-	elseif ( $post == $post_obj->post_name )
+	elseif ( in_array( $post_obj->post_name, $post ) )
 		return true;
 
 	return false;