fancybox iframe multiple requests

Question

I have a list of items. Each item has a button that opens a new page in an iframe. This iframe is handled using fancybox jquery lightbox.

The fancybox code is here:

$(".CheckOutContainerUR").fancybox({
            scrolling: 'no', hideOnContentClic: false, enableEscapeButton: true, autoSize: true, scrollOutside: true, title: null, 
            afterClose: function () {
                <%=Page.ClientScript.GetPostBackEventReference(ContainerUCCUpdatePanel, "UCDC")%>
            }
        });

The list of items is hosted inside an updatepanel, and after closing the fancybox the update panel is updated.

First item clicked opens the iframe with the page as expected, but any further clicks multiplies the number of requests, and I cannot figure out the reason.

The item element from the list looks like this:

<a runat="server" data-fancybox-type="iframe" href='<%# string.Format("~/UI/iActions/Container/iCheckOut.aspx?cid={0}", Eval("container_id")) %>'  
                                                        id="A2" tag='<%# Eval("container_id")%>' class="mini actionButton silver CheckOutContainerUR" 
                                                        title="Check out the container" style="cursor: pointer;">Check Out
                                                    </a>