Well, it is difficult to fix if one wants to make it right...
you can do the following trick in media/com_hotspots/js/modules/hotspot.js on line 347 you have
right after that line add:
window.fireEvent('openUniqueInfoWindow', hotspot.id);
this should do it, but I don't like it because what we do is to repeat an ajax request.
When you click on a marker we do an ajax request to get the data for the infowindow. Normally when you zoom in, we don't do anything -> we just keep it open.
But with the above solution you'll zoom in and we tell the hotspot module -> load again the infowindow -> we start an ajax request and when it finishes we move the map so that the infowindow is centered. I won't add this in the next release, but you can hack the file if you want.
Regards,
Daniel