Taking pictures with headphone jack

It's a first generation Moto G running Android 5.0.2 and I'm trying to make this [headphone-jack selfie stick](http://www.amazon.ca/Selfie-Stick-JETech%C2%AE-Battery-Free/dp/B00VYX95T4) work. Tried with both Motorola Camera and Google Camera apps. Both take photos correctly when the volume button is pressed on the phone. Neither take a photo when the button on the selfie stick is pressed. I would consider the product defective, but Google Camera actually focuses when the button is pressed. Is there any setting I'm missing, or a way to find what the selfie stick button is actually doing so I can re-map the action?