I had uninstalled LCC (Logitec Control Center) for maybe 3 weeks. I got tired of the missing functionality of the many extra buttons on my MX-1100 mouse, so I reinstalled LCC again. Now the 'jumpy lines' happen much less. Now it may be one line jumps down in after a minute. Before it was 1-3 lines every 10 seconds. I can live with the anomaly easier now.