Analog input, different values on pins 14 and 15

Hi,

I have found I am getting different values from analog pins 14 and 15 on my arduino mega when compaired to all other analog pins.
I found the problem when building my reprap 3d printer, which uses pins 13, 14 and 15 for temperature measurment. I have also built a simple voltage divider and printed the analog value to serial to test all the analog pins, and 14 and 15 give different values with exactly the same circuit.

Anybody any ideas what is causing this?

thanks

Andy

What resistor values are you using for your voltage divider testing?

Im using a 1k and 10k resistor and a 5v input. If my math is correct this should give me an output voltage of 0.45.
im using code copied from here http://arduino.cc/en/Tutorial/ReadAnalogVoltage.
I reading 0.43 on all but pins 14 and 15, where I get 3.55 and 1.35.

Take your divider out. What happens when connected to 0V and 5V?

I get 5 and 0 when connected to 5V and ground.