ofAppGLFWWindow: Non-working multi display fullscreen (Archlinux)

I'm trying to get multi monitor fullscreen to work. I'm using the following in main.cpp

#include "ofMain.h"
#include "ofApp.h"
#include "ofAppGLFWWindow.h" 

//========================================================================
int main( ){
       ofAppGLFWWindow window;  
       window.setMultiDisplayFullscreen(true);  
       ofSetupOpenGL(&window,1024,768,OF_FULLSCREEN);  
    
	ofRunApp( new ofApp());
}

The fullscreen simply does not extend beyond one screen.

This issue occurs with both oF 0.9.8 and the 20161216 nightly.
(In oF 0.9.8, I'm not even able to make a non-fullscreen window that is larger than the first screen width ofSetupOpenGL(&window,2300,768, OF_WINDOW);, but this one does work in the nightly.)

Probably related: #5009, #4498 and especially #4698.

I'll try on Windows later today. I'm using Arch Linux w/ KDE, GLFW 3.2, Nvidida.

Start with the main.cpp setup using ofAppGLFWWindow::setMultiDisplayFullscreen and ofSetupOpenGL, then reproduce it on Arch Linux with KDE, GLFW 3.2, and Nvidia. Compare fullscreen and oversized-window behavior between 0.9.8 and the nightly, and review issues #5009, #4498, and #4698. Done means fullscreen spans the displays and the reported window sizing behavior is resolved.