[randallsquared]

> For some reason the OS needs to disable/reset all displays [...]

Yes, I hate this. Also, many monitors do not like whatever the Mac is doing, and will tolerate it only a small integer number of times before you have to interrupt power to them for a reset.

> You cannot drag fullscreen windows from one monitor to another. You cannot drag a non-fullscreen window to a monitor which has a fullscreen window.

I was actually replying to insist that you can, but then I realized (just now) that you said "monitor", not "desktop", so I'm not sure that this would work. Does it work for you with desktop spaces? 'Cause it does for me, although it makes the incoming window a chromeless as well and tiles with the existing window, which I didn't really expect.