细胞边界在结束时保持开放状态？

Question

查看最后的单元格边框是如何打开的。原因是什么？这是代码：

<td class="center" style="width: 50%;">
    <table class="heading_table">
        <tr>
            <th>Workload Year</th>
            <td>${scenario.workloadYear}</td>
            <th>SORs</th>
            <td class=”wrappable”> 
            <c:forEach items="${scenario.sorCodesNames}" var="item" varStatus="status"> 
            ${item}
            <c:if test= "${!status.last}">,</c:if>
            </c:forEach>
            </td>
            </tr>
            <th style="text-align: center; font-weight: normal;" colspan="6">
                Last modified by <strong>${scenario.auditable.lastModifiedBy.lastName}, ${scenario.auditable.lastModifiedBy.firstName}</strong>
                on <fmt:formatDate value="${scenario.auditable.lastModifiedDate}" pattern="${date_time_pattern}" />
            </th>

    </table>

/* Style applied to all header cells within a heading_table. */
table.heading_table th
{
    text-align: left;
    font-size: 10pt;
    font-family: arial, sans-serif;
    border: #999999 1px solid;
    background-color: #E8E8E8;
    padding-left: 8px;
    padding-right: 8px;
    padding-top: 3px;
    padding-bottom: 3px;
    margin: 0px 50px 0px 0px;
    white-space: nowrap;
}
/* Style applied to all data cells within a heading_table. */
table.heading_table td
{
    text-align: left;
    font-size: 10pt;
    font-family: arial, sans-serif;
    border: #999999 1px solid;
    background-color: #ffffff;
    padding-left: 8px;
    padding-right: 8px;
    padding-top: 3px;
    padding-bottom: 3px;
    margin: 0px 50px 0px 0px;
    white-space: nowrap;
}

Answer 1

<td class="center" style="width: 50%;">
<table class="heading_table">
    <tr>
        <th>Workload Year</th>
        <td>${scenario.workloadYear}</td>
        <th>SORs</th>
        <td class=”wrappable”> 
        <c:forEach items="${scenario.sorCodesNames}" var="item" varStatus="status"> 
        ${item}
        <c:if test= "${!status.last}">,</c:if>
        </c:forEach>
        </td>
     </tr>
     <tr>
        <th style="text-align: center; font-weight: normal;" colspan="6">
            Last modified by <strong>${scenario.auditable.lastModifiedBy.lastName}, ${scenario.auditable.lastModifiedBy.firstName}</strong>
            on <fmt:formatDate value="${scenario.auditable.lastModifiedDate}" pattern="${date_time_pattern}" />
        </th>
      </tr>
</table>