Problem with GpsMap 276C NMEA PORTS 1 and 2

According the specifications found in the Garmin Home Page, the
GpsMap 276C has TWO NMEA serial Ports (1 and 2), and these are in
addition of another USB port.

But when I set one of the two serial ports to NMEA, the software
switches the other serial port to NONE, that is, I can not have both
2 SERIAL ports,1 and 2, set as NMEA. But the manual implies that
this is possible.

I think this could be a software problem, as does not make sense to
have 2 serial NMEA ports and allowing the user to use only one.

The same specification of the two serial ports supported in the
GpsMap 3006/3010 is explained more clearly in that unit's manual,
pages 72-74.

Any coments?