NVIDIA firmware update [0] solved the problem for me. It seems they ditched the naughty part of DisplayPort standard for good and stopped passing hot-plug events to OS.
Sometimes I can't get to them at all on the laptop screen without forcing it closed and reopening.
The regular [win] + [left/right] for snapping to 1/2 screen positions will also move it across screens if you hit it repeatedly.
Sadly MS figured we all wanted to have to shit move around as soon as you use a KVM.
(Also, there's usually a 90% chance that windows will not correctly handle the monitor reconnecting without having to either power cycle the monitor or using the video card's 'really truly scan for monitor changes' feature.)
[0]: https://superuser.com/questions/630555/turning-displayport-m...
Waking from sleep will periodically just not find a monitor at all, or they will come up with the wrong positioning (left and right swapped). If I turn a monitor off, the other one (and the laptop) do some sort of resync operation that interrupts the display. It's annoying, but not something I would expect the industry to consider a priority; I'm not really sure it's a monitor issue at all.
So yeah, it's better than when off really meant off and ports lacked cable detection.