Cannot remove donation from cart

Setup: Drupal 6.9, Ubercart 6.x-2.0-beta3, and uc_donation 6.x-2.x-dev from 2009-02-09.

To reproduce.

1. Install and enable above modules
2. Create a donation page
3. Go to donation page, enter a value and click "add to cart"
4. Check "remove from cart" checkbox at example.com/cart and click "Update cart"

Expected result : empty cart
Actual result: donation with a value of $0.00 which prevents the user from checking out as submitting produces the following error:

 "You have entered an invalid amount."

NOTE:

I have added the following to my template.php file To avoid the call to undefined user function error that occurs when viewing the donation node.

warning: call_user_func_array() [function.call-user-func-array]: First argument is expected to be a valid callback, 'uc_product_add_to_cart_form_93' was given in .../form.inc

<?php
function phptemplate_uc_product_add_to_cart($node, $teaser = 0, $page = 0) {
	$output = '<div class="add_to_cart">';
	$output .= drupal_get_form('uc_product_add_to_cart_form', $node);
	$output .= '</div>';
	return $output;
 }
?>

Removing this override does not seem to affect the the ability to remove unwanted donations from the user's shopping cart.