warning! train jumped from <berth> to <same berth> (expected from NIL)!

trackernet.lisp

@@ -4537,7 +4537,7 @@ Return four values: a set of nodes, edges, weights, and a new->old edge mapping.
       ;; HACK(eta): clobber any existing entry for this timestamp, in order
       ;;            to deal with really fast berth stepping
       (red:zremrangebyscore (format nil "X-train-~A" headcode) ts ts)
-      (when (and last-entry
+      (when (and last-entry old-berth
                  (not (string= (track-code (cadr last-entry)) old-berth)))
         (log:warn "train ~A jumped from berth ~A to ~A (expected from ~A)!"
                   headcode (track-code (cadr last-entry))