[GPSNavX]

If you have "Pos.icon.Loc." set to "Ctr" or "Offset", iNavX will automatically load/display the next NOAA raster chart as your iDevice position changes. So my guess is there is something in the NMEA stream being provided to iNavX that is giving an erroneous lat/lon and as such iNavX believes you have navigated off the current NOAA chart and it finds the only chart with the erroneous position is the world chart.