Thank you so much for posting this. I don't have an answer but I had the same problem and your method for fixing it works for me...it was driving me NUTS!!!!! Thanks again.
Seems like a classic software jitter problem. My guess is that you'll have a really hard time getting the job done in a reliable way unless you switch to a real time operating system. Try killing every process you can from the System Tray and Task Manager and see if that helps.