UI and multiple displays

I'm working on a project in Unity 5.3 w/ multiple display support. I'm rendering a separate canvas to each display in fullscreen native resolution. The idea is that one display is a touchscreen for input while the other is a regular non-touch display for output.

Everything works great in the editor. When running a build, everything displays well, but no input from the touchscreen is registered when touching UI buttons.

I found...

UI and multiple displays