HTML5拖放jQuery UI对话框

Question

我正在阅读博客http://swiftbend.com/blog/?page_id=188#.VBHsLvl5Pft，我想将图片拖到模态窗口上。我遇到的问题是，当我将图像拖放到模态窗口时，图像占据了整个页面。

<div id="popupdiv" title="Basic modal dialog" style="display: none">
<table id="tbAttach" style="margin: 10px 0; width: 100%; display: block; font-size:0.9em;">
    <thead class="ui-widget-header">
         <tr>
            <th class="ui-state-default">File Name</th>
            <th class="ui-state-default">Image</th>
            <th class="ui-state-default">Delete</th>
        </tr>
    </thead>
    <tbody class="ui-widget-content">
        <tr>
            <td></td>
            <td>
                <div class="filedrop" draggable="true" style="display: block;"></div>
            </td>
            <td></td>
        </tr>
        <tr>
            <td></td>
            <td><div class="filedrop" draggable="true" style="display: block;"></div></td>
            <td></td>
        </tr>
        <tr>
            <td></td>
            <td><div class="filedrop" draggable="true" style="display: block;"></div></td>
            <td></td>
        </tr>
    </tbody>
</table>

<asp:ImageButton ID="DetailQuery" runat="server" ImageUrl="~/Images/imgDetails.gif" OnClientClick='<%# "return Backup(" + Container.DataItemIndex + ")" %>' >

function Backup(position) {
    $("#popupdiv").dialog({
            title: "Backup",
            width: 520,
            height: 350,
            modal: true,
            buttons: {
                Close: function () {
                    $(this).dialog('close');
                }
            }
        });            

    }