I have done quite a lot of googling, and found nothing, so I'm hoping some of the experts on here can help.... I have a Macbook Pro - a new 15" touchbar retina &c &c model. When I work from home, I plug a monitor in, so I have two displays - my Macbook screen, and my HDMI monitor. I have "Displays have separate spaces" selected in the Mission Control preferences, so that I can (for example) keep one programme open on the second monitor, and it's always visible whichever space my Macbook screen shows. All fine so far. BUT - when I select to activate the programme on the second monitor, the desktop space on my Macbook switches too! I have tried enabling/disabling the "When switching to an application, switch to a Space..." option, and it has no difference. This doesn't happen with every program: the main culprit seems to be NoMachine Player (used for remote connections to work). Indeed, when I select NoMachine, the menubar on the HDMI screen still shows "Finder" and the menubar on my macbook screen shows the NoMachine menu! This suggests somehow dragging the NoMachine window over to the second screen didn't cause OSX to recognise the app as being on that Space. I have tried killing NoMachine, and launching it explcicly on the second display (i.e. two-finger click on the dock icon -> options -> display on desktop 2). It makes no difference. I realise this is likely a fairly unique problem, specific to the NoMachine / OSX combinastion, but does anyone have any ideas? I've had this problem with my current MBP, a 2012 retina MPB (15") and certainly for El Capitain and Sierra, I can't remember older OSes!