NI 9269 AO: Set output to high impedance

I'm using the NI 9269 module in a cDAQ-9185. When the cDAQ boots, the 9269 output is high impedance (~280k ohms), as specified in the datasheet. However, as soon as I do anything on the cDAQ chassis (including reading AI from the adjacent NI 9205 module have), the output goes to low impedance (0.1 ohms on handheld multimeter). 

I've tried "DAQmx Reset Device" to no effect (just sets the output to zero). It seems I have to reboot the entire cDAQ chassis to get it to go back to high impedance.

So, how do I set the output of the NI 9269 to high impedance (in a cDAQ chassis)?

SW:

DAQmx 17.5

LabVIEW 2017

C# drivers written for DAQmx drivers (my real use-case, I'm just trying things out in LabVIEW)

Use-case:

I have a test case where an AO channel on the 9269 is active low - meaning I can't just write zero to the output to "turn it off" so to speak.