I figured out something similar, but I am having issues that the latitude of the coordinates seem to be wrong on macOS at least. Basically my markers appear a bit below the clicked coordinate (unless I turn off the toolbar, in which case they appear at the mouse location but we are talking about the top of the balloons, not the little bottom arrow part). I suspect there is an issue with converting the coordinates using .local caused by the height off toolbars and the window frame. It seems I get the correct latitude if I hide the toolbar and expand the window to fullscreen.