Bug at datetime_select when used with object[] to submit multiple model

It seems like something is wrong with the datetime_select helper. the
helper does not generate name as object[][field(1i)], instead it
generates object[field(1i)], which results a 500 error as follows:

Conflicting types for parameter containers. Expected an instance of
Hash but found an instance of Array. This can be caused by colliding
Array and Hash parameters like qs[]=value&qs[key]=value. (The
parameters received were [{"name"=>"", "description"=>""}].)

I have tested both date_select and datetime_select suffer from the
same issue, anyone can confirm that?

To let everyone understand the issue clearly, here is the sample:

<% form_for "task[]", @task,:url=>{:action=>'save_create_multi'} do |
form> %>
    <% (1..10).each do %>
    <p>
    <%= form.label :name, "Name"%>
    <%= form.text_field :name %>
    <%= form.label :description, "Description"%>
    <%= form.text_field :description %>
    <%= form.label :due_date %>
    <%= form.date_select :due_date %>

    </p>
    <% end %>
    <%= form.submit 'Save' %>
<% end %>

And the generated HTML:
<p>
    <label for="task__name">Name</label>
    <input id="task__name" name="task[][name]" size="30" type="text" /

    <label for="task__description">Description</label>
    <input id="task__description" name="task[][description]" size="30"
type="text" />
    <label for="task__due_date">Due date</label>
    <select id="task_due_date_1i" name="task[due_date(1i)]">
<option value="2003">2003</option>
...

Notice the due_date part does not have the extra empty square bracket.