Index: wp-includes/comment.php
===================================================================
--- wp-includes/comment.php	(revision 17367)
+++ wp-includes/comment.php	(working copy)
@@ -1326,8 +1326,10 @@
 	$commentdata['comment_author_IP'] = preg_replace( '/[^0-9a-fA-F:., ]/', '',$_SERVER['REMOTE_ADDR'] );
 	$commentdata['comment_agent']     = substr($_SERVER['HTTP_USER_AGENT'], 0, 254);
 
-	$commentdata['comment_date']     = current_time('mysql');
-	$commentdata['comment_date_gmt'] = current_time('mysql', 1);
+	if( empty( $commentdata['comment_date'] ) || ! strtotime( $commentdata['comment_date'] ) )
+		$commentdata['comment_date'] = current_time('mysql');
+	if( empty( $commentdata['comment_date_gmt'] ) || ! strtotime( $commentdata['comment_date_gmt'] ) )
+		$commentdata['comment_date_gmt'] = current_time('mysql', 1);
 
 	$commentdata = wp_filter_comment($commentdata);