Index: post.php
===================================================================
--- post.php	(revision 19926)
+++ post.php	(working copy)
@@ -3632,15 +3632,6 @@
 	if ( ! in_array( $post_status, array( 'inherit', 'private' ) ) )
 		$post_status = 'inherit';
 
-	// Make sure we set a valid category.
-	if ( !isset($post_category) || 0 == count($post_category) || !is_array($post_category) ) {
-		// 'post' requires at least one category.
-		if ( 'post' == $post_type )
-			$post_category = array( get_option('default_category') );
-		else
-			$post_category = array();
-	}
-
 	// Are we updating or creating?
 	if ( !empty($ID) ) {
 		$update = true;
@@ -3723,8 +3714,6 @@
 		$wpdb->update( $wpdb->posts, compact("post_name"), array( 'ID' => $post_ID ) );
 	}
 
-	wp_set_post_categories($post_ID, $post_category);
-
 	if ( $file )
 		update_attached_file( $post_ID, $file );