Index: wp-admin/includes/post.php
===================================================================
--- wp-admin/includes/post.php	(revision 19762)
+++ wp-admin/includes/post.php	(working copy)
@@ -223,6 +223,10 @@
 		}
 	}
 
+	// Drafts shouldn't be assigned a date unless explicitly done so by the user
+	if ( in_array( $post_data['post_status'], array( 'draft', 'pending', 'auto-draft' ) ) && !empty( $post_data['post_date'] ) && $post_data['post_date'] == $post->post_date )
+		$post_data['post_date_gmt'] = '';
+
 	add_meta( $post_ID );
 
 	update_post_meta( $post_ID, '_edit_last', $GLOBALS['current_user']->ID );