SUBMIT in hook_view() to itself

I'm writing my own module called say "xmodule". I ran into a problem while implementing hook_view() which contains a submit action/button to itself (hook_view()). To wit, when I insert an submit button like this:

function xmodule_view(&$node, $teaser = FALSE, $page = FALSE) {
  ...
  $form .= form_submit(t('Toggle details'));
  ...
  $output .= form($form, 'post');
  $node->body = $output;
}

.. and then click on the button "Toggle details", the listing of all nodes is being shown (the effect is as if ?q=node is being executed). However, the url field in my browser still shows ?q=node/19, which matches the ACTION value in form tag.

Can anybody shed some light on this behaviour? Thanks.