I have a similar problem with Google maps API V3 - multiple markers on exact same spot. I have read @ DzinX 's answer and try to use it. But it seems my lat and lng cannot use "+". But when i try "*", it worked. The datatype of lat and lng is float(tried double and decimal also). Any reason why?
for (var i = 0; i < locations.length; i++) {
lat = locations[i][0];
lng = locations[i][1]
var marker = new google.maps.Marker({position: new google.maps.LatLng(lat*2, lng), icon: 'images/markers_red.png'
});
markers.push(marker);
marker.setMap(map);
}