By default when you click on a push pin it actually cancels the popup.
Use this instead:
function AddClickablePin(location, icon_url, title, details, iconStyle)
{
var pin = new VEPushpin(pinID, location, icon_url, title, details, iconStyle);
map.AddPushpin(pin);
var element = document.getElementById(pinID);
element.onclick = EventHandlerOnClick;
pinID++;
}
function EventHandlerOnClick(e)
{
if (e!=null)
{
document.getElementById(e.currentTarget.id + "_" + map.GUID).onmouseover();
} else
{
document.getElementById(window.event.srcElement.id).onmouseover();
}
}