[GPSNavX]

When ever a waypoint is activated (i.e. Goto) either manually or automatically XTE (Cross Track Error) is reset to 0. One thing that comes to mind is possibly there is so much NMEA data buffered up in a multiplexer or in the autopilot that it is lagging behind what MacENC is displaying. To minimize the amount of NMEA data sent to the Autopilot make sure "Autopilot Only" is checked in the GPS panel Settings drawer.