I am having a similar problem. The LadyAda Motor shield does not use the Analog pins A0-5 . When I have the LadyAda Motor shield unplugged the sensor I use in Analog A0-5 work as expected. When the Motorshield is plugged in the wires seem crossed between A0 and A1 and sometimes other pins. My motor shield is plugged into a different set of batteries, the Arduino is plugged into the USB. If someone has come up with an explanation I would love to hear it. Thanks in advance. The thanks after are coming too.