Thanks, Dominik. However, that doesn't seem to work: on your JSFiddle, the map is never plotted (while the browser tab consumes most of my CPU). In my own app, the maps render but the new onClick functions make no difference AFAICS, whether I zoom using the buttons or the mouse.
In the mappie examples on the Highcharts site and elsewhere (including the canonical example at
https://www.highcharts.com/demo/maps/map-pies), this onClick code isn't used but the pie charts still redraw in their correct locations after a zoom (by button or mouse). Some, but not all, examples have a 'render' method in the initial seriesType definition, but this fails in my own code with "Cannot read property 'is' of undefined" on the line "if (series.group && linkedSeries.is('map'))" so I excluded it. Might this be the cause, and do you know what the problem is with the code if so?
I also did see that, on JSFiddle (but not my own code), there's an error in the console from my original code 'fathom is not defined'. I've no idea what this means but might it be related?