也许我在这里弄错了，您将其他所有表单元素都设置为要放入数组中，除了 delete_id.delete_id 应该是这样形式的数组吗?

Maybe I'm mistaken here, you set every other form element to be put into an array EXCEPT delete_id. Is delete_id supposed to be an array in the form like so?

<li>
    <input type="text" name="file[]" size="25" />
    <input type="text" name="case[]" size="25" />
    <input type="text" name="name[]" size="25" />
    <input type="hidden" name="delete_id[]" value="' . $row['cases_id'] . '" />
</li>

<li>
    <input type="text" name="file[]" size="25" />
    <input type="text" name="case[]" size="25" />
    <input type="text" name="name[]" size="25" />
    <input type="hidden" name="delete_id[]" value="' . $row['cases_id'] . '" />
</li>

<li>
    <input type="text" name="file[]" size="25" />
    <input type="text" name="case[]" size="25" />
    <input type="text" name="name[]" size="25" />
    <input type="hidden" name="delete_id[]" value="' . $row['cases_id'] . '" />
</li>