回声有时会起作用，有时它不会 - 为什么？

Question

使用download.php表单 - 不起作用 使用remove.php执行表单 - 工作

我错过了一些小事吗？

<table id="mytable1" width="80%"  class="text-center table table-striped table-bordered table-Responsive ">
    <thead>
    <th>File Name</th>
    <th>File Type</th>
    <th>File Size(KB)</th>
    <th>Remove</th>
    <th>Download</th>
    </thead>
    </tr>

<?php
    while($item = mysql_fetch_array($result1)) {
        echo "<tr>";
        echo "<td>".$item['file_name']."</td>";
        echo "<td>".$item['file_type']."</td>";
        echo "<td>".$item['file_size']."</td>";

    // this command does not work but the next echo works - why?
        echo "<td><form action='download.php' method='GET'><input name='filename' type='hidden'  value='".$item['file_name']."'/><button  class='btn btn-danger btn-xs' type='submit' value='down'/><span class='glyphicon glyphicon-trash'></span></form></td>";

        echo "<td><form action='remove.php' method='GET'><input name='filename' type='hidden'  value='".$item['file_name']."'/><button  class='btn btn-primary btn-xs' type='submit' value='del'/><span class='glyphicon glyphicon-download'></span></form></td>";

        echo "</tr>";
    }                   
    echo "</table>";
?>