Why are the Google Maps Marker and InfoWindow not centered?

i make a map with this code

var map;
var myOptions = {
    center: new google.maps.LatLng(-31.403759,-64.174232),
    zoom: 12,
    panControl: true,
    zoomControl: true,
    mapTypeControl: true,
    scaleControl: true,
    streetViewControl: true,
    overviewMapControl: true,
    mapTypeId: google.maps.MapTypeId.ROADMAP 
};

function iniciar() {
    map = new google.maps.Map(document.getElementById("map"),myOptions);
}

function marcar(lat, lng) {
    var contentString = '<div id="content">'+
        '<div id="siteNotice">'+
        '</div>'+
        '<h1 id="firstHeading" class="firstHeading">Uluru</h1>'+
        '<div id="bodyContent">'+
        '<p><b>Uluru</b>, also referred to as <b>Ayers Rock</b>, is a large ' +
        'sandstone rock formation in the southern part of the '+
        'Northern Territory, central Australia. It lies 335 km (208 mi) '+
        'south west of the nearest large town, Alice Springs; 450 km '+
        '(280 mi) by road. Kata Tjuta and Uluru are the two major '+
        'features of the Uluru - Kata Tjuta National Park. Uluru is '+
        'sacred to the Pitjantjatjara and Yankunytjatjara, the '+
        'Aboriginal people of the area. It has many springs, waterholes, '+
        'rock caves and ancient paintings. Uluru is listed as a World '+
        'Heritage Site.</p>'+
        '<p>Attribution: Uluru, <a href="http://en.wikipedia.org/w/index.php?title=Uluru&oldid=297882194">'+
        'http://en.wikipedia.org/w/index.php?title=Uluru</a> (last visited June 22, 2009).</p>'+
        '</div>'+
        '</div>';
    var infowindow = new google.maps.InfoWindow({
        content: contentString
    });
    var location=new google.maps.LatLng(lat,lng);
    var marker = new google.maps.Marker({
        position: location, 
        map: maps
    });
    google.maps.event.addListener(marker, 'click', function() {
        infowindow.open(map,marker);
    });
}

When I try to click on markers, they are decalibrated so that when I click on the center of a marker nothing happens. But a few centimeters down, a cursor appears like the marker is at that point.

So the map is not centered and the marker appears at the real coordinates, but I have to click 2 cm down away from the marker for the click on the marker...

Why is that?? Has anybody else had this happen??