Google Maps API v3 - Tiles turn gray when selecting area (but map is still visible underneath the gray)

Google Maps API v3 - Tiles turn gray when selecting area (but map is still
visible underneath the gray)

When selecting an area in my google maps application, some tiles turn
gray. The map underneath stays visible. I am not using any functions or
methods that handle tiles, so I have no idea where to look for the cause.
The internet was not a big help so far. Can somebody please help me to
squash this annoying bug :p?
Ps: I have never coded javascript before, just been doing that for about 4
days, so that might explain my low level of expertise on the subject;
hopefully it's just a small thing...
/// <reference path="google-maps-3-vs-1-0.js" />
google.maps.visualRefresh = true;
var global = this;
var map;
var center;
var geocoder;
var country = 'Belgium';
var fMapBounds = new google.maps.LatLngBounds();
var curZoomLevel, prvZoomLevel;
var markers = [];
var icons = [];
var recSelectActive = true;
// Initialize
//#region
function initialize() {
// Create map + center (this center must be done before adding markers)
curZoomLevel = 8;
var mapOptions =
{
center: new google.maps.LatLng(50.0, 5.0),
zoom: curZoomLevel,
mapTypeId: google.maps.MapTypeId.ROADMAP,
mapTypeControl: false,
panControl: true,
panControlOptions: { position:
google.maps.ControlPosition.TOP_RIGHT },
zoomControl: true,
zoomControlOptions: { style: google.maps.ZoomControlStyle.LARGE,
position: google.maps.ControlPosition.LEFT_CENTER },
scaleControl: false,
streetViewControl: false
};
map = new google.maps.Map(document.getElementById('map-canvas'),
mapOptions);
map.setCenter(center);
// Create all pins for performance reasons
//#region
createPins();
//