Noisy log data over USB link

On a recent MacBook Pro (Retina) running latest Mavericks, I observe errors in downloading dataflash logs ; I don’t see this on a much older Windows 7 machine. For example, a 2MB log produces 60 corrupt line warnings on the Mac, while the same log gives only 5 line errors on the Windows machine. I’m running the latest APM Planner 2.0.9 on both. Mavlink link status on Mission Planner on the Windows machine also reports no errors.
The APM 2.6 is running very recent firmware.
Any ideas of what might be causing these serial line errors, and how they might be eliminated?

What version of FW on the APM2.6

Can you post logs with the errors in?

Also, how did you download, using Terminal or the MAVLink log download interface? look at Graphs view for this option