Maybe 
MS would probably tell us the windows arenāt ālostā, theyāre just taking a break from all the attention for a bit of R&R.
I had chalked it up to Java, not having tried it on another OS. Ignition Designer gets confused about what size is actually maximized on multiple monitors of different sizes and will maximize on a large connected monitor to the size of my laptop display. Child windows like Tag Editor, Property Binding, and Translation Manager remember where they were last open (handy if still on the same monitor setup), and will open there again whether thereās a monitor there or not. This is a pain as I havenāt found a way to get them back (donāt show on taskbar as OP noted) other than plugging in a monitor so I can drag 'em home. All that said, Iād still far rather work with Ignition than any of quite a number of other HMI packages Iāve used that seemed to cooperate better with MS window/monitor management.