I am using the 900HP/programmable's pins 6 (DIO10,PWM0) and 7 (DIO11,PWM1), which Digi documents as a bidirectional GPIO, as a digital input. I have verified with a meter that both output VCC in their normal states through the internal pull-up.
The application of the inputs is to detect a maintained (at least a couple seconds) transition to LOW. This is done by submersion of a pipe with two probes attached, into water, whose conductive vessel is ensured a chassis-bonded path to GND(common to Pin #10/GND).
Whenever the bottom probe, Pin6/DIO10/PWM0 touches the water and goes to ground, it works.
Whenever the top probe, Pin7/DIO11/PWM1 touches the water and tries to ground, it doesn't work.
Whenever the top probe is shunted to Pin 10 / GND via some hookup wire, it works fine.
At first I thought this was a resistance issue through the fluid medium, but DIO10 works just fine. I have tried reconfiguring "Drive Strength" in the Smart editor in both High and Low, and this does not make a difference (though I think that is only relevant when the pin is configured as an output anyway.)
What could be causing this?