Zoom Window should ‘ignore’ the ‘virtual’ ground plane. It’s impossible, for instance, to zoom in to detail of an object standing on the ground plane, if a part of the ground plane is ‘visible’ in the zoom window.
Philip
Checking it - thanks.
So far I do not see anything amiss - I have a box on the GP and I start Zoom, make a window around a corner of the box - it zooms as expected so far…
-Pascal
I realise now that it was a really bad explanation… Sorry! Zooming isn’t the problem, but rotating the view after zooming in to a detail (in the perspective viewport) - the target seems to be on the ground plane and not the object, which means that when I rotate the view the object disappears sideways out of view.
Philip
Hi Philip - I don’t know if there is a bug here, I’ll fool around with it, but, as a general purpose zoom tool, Zoom Target is much more effective, in my experience. I changed my Z+ Enter to fire off Zoom Target rather than Zoom
-Pascal
I don’t think it’s a bug either - probably intended behaviour, but I personally just don’t like it in combination with a ‘virtual’ ground plane. It makes working a bit more difficult than it need to be. I know Zoom Target gets around this problem and I use that a lot also. However… 
Zoom Window is often a bit easier to use as you don’t have to snap to anything. Of course I could use Zoom Target without snapping to the object, but then it behaves as badly as Zoom Window in combination with the ground plane.
Philip