Hi Harry,
My feeling is that the WHOLE of PI 'loses focus' at the end of the application of a Process - with the Taskbar icon flashing 'orange' at the bottom of the screen.
I think that this might explain why your 'image' has to be 'clicked' to send keyboard commands to it - you are actually bringing focus back to PixInsight itself.
Is anyone else seeing this sort of behaviour?
(Oh, and remember Harry, you can Zoom in and out with the mouse ScrollWheel, and you can 'PAN' the image with the ScrollWheel pressed whilst moving the mouse)
Cheers,