Ah, I thought you were displaying on both outputs, not switching between them, hence my mirroring comment. I suspect XFCE, not the DM, detects the output change and takes care of it. You might need to emulate that behavior with a hook of some type that you have to setup yourself with the tiling WM, and you might have to –off the unused display. I’d be willing to bet you can find some sort of hook script out there that can do this, I seem to recall an autorandr program I used in the past where you could set up output profiles. I hope that helps, maybe a little bit.