为什么当我调用AJAX方法时动画GIF没有动画?

使用下面的代码，我可以使对话框在加载AJAX数据时正确显示，但是动画GIF没有动画-看起来很烂.

Using the code below, I can get the dialog to display properly while the AJAX data loads, but the animated GIF is not animated - looks really crappy.

CSS:

.loading {
    background: url('/images/loading.gif');
}

JavaScript:

JavaScript:

$(function() {
    $("#createButton").click(function(e){
        e.preventDefault();

        var $form = $(this).closest("form");

        $("#pleaseWait-dialog").dialog({
            modal: true,
            height: 200,
            resizable: false,
            draggable: false
        });

        $.ajax({
            type: "GET",
            url: "myScript.cfm",
            async: true,
            success: function() {
                $form.submit();
            }
        });

        return false;
    });
});

HTML:

<form action="post.cfm" method="post">
    <input
        id="createButton"
        type="submit"
        name="createButton"
        value="Create a New Thing" />
</form>
<div id="pleaseWait-dialog" title="Gathering Data" style="display:none;">
    <span class="loading"></span>
    <p>Thank you for your patience while we gather your data!</p>
</div>