XBee S2 Analog Pin Readings

I have 2 XBee S2 routers. The settings for Analog Pins 0 thru 3 are set to ADC [2]. One XBees is mounted on a Jaycon Systems explorer board and the other on an adapter board.

Currently I have nothing attached to the sensor pins, just configured. The samples for the pins are all coming into my Netduino as follows:

Analog Pin 0 0211 = ( 529 0.62052785923753662 )
Analog Pin 1 0210 = ( 528 0.61935483870967745 )
Analog Pin 2 020E = ( 526 0.61700879765395888 )
Analog Pin 3 020F = ( 527 0.61818181818181817 )

I was expecting them to be 0 since nothing is connected.
Am I missing something in my understanding here? I am afraid to connect sensors in that I might send too much voltage & burn out the pins.
Thanks for your thoughts.

That would indicate that you are getting voltage on the lines. Regardless of what you think.

Is that normal for the adapter boards to do this?

If the analog inputs are not connected they may float. You should connect them to GND your ADC should read 0x00. If you connect them to VCC your ADC should read 0x3FF.