In Rhino 8 and Rhino 9 BETA the Details on the active Layout are regarded as “Viewports” when you fx Zoom Extents All Viewports, but they are NOT regarded as Viewports when you change your Grid settings in one Detail and choose to Apply to All Viewports and not only the active Detail. It has never worked as you would expect in Rhino 8, but there might be time to fix this in Rhino 9 BETA?
GridChangeInAllViewports.3dm (215.8 KB)