strange behavior with form in computed field

I'm using a computed field to display a form on a node view only to registered users. The form is in a custom module i've written. I simply do a check for user_logged_in and if TRUE then I call drupal_get_form() to display the form.

The form displays properly but the validate and submit functions are not called. However if I submit the modules form (admin/build/modules) then the form will behave as expected once. If I navigate back to the node with the form computed field it will neither validate nor submit until I resubmit the modules form.

Very strange.

Even stranger, if I include a text area field and paste in the same code (with minor alterations to just print the form), then the computed field always behaves as expected.
Finally, if I configure the field to be stored in the database, then the form renders twice in the node view.

Here is my code included in the computed field:

// get the license string
include('./' . drupal_get_path('module', 'saybit_com_downloads') . '/includes/'.$node->field_license_file[0]['value']);

// add HTML to indicate need to agree to the license to download
$node_field[0]['value'] .= '<h2>License Agreement</h2><p>In order to download, please read the following license agreement and agree by checking the checkbox. Then click the download button.</p>';
if (user_is_logged_in())
{
  $node_field[0]['value'] .= drupal_get_form('saybit_com_downloads_download_form_with_license', file_directory_path().'/private/'.$node->field_download_file[0]['value'], $license);
}
else
{
  $node_field[0]['value'] = '<p>You must have be logged-in to download this file.</p><div><a 

  href="/login" target="_blank">log-in</a></div><div><a href="/register" 

  target="_blank">register</a></div>';
}

Any insight would be greatly appreciated.

Thanks!
Ted