That '1' should be in a quantity box.

In your source, it looks like this:

1<input type="hidden" name="cart_quantity[]" value="1" /><br /><span class="alert bold"></span><br /><br /> </td>


In a stock Zencart installation, the 'type=hidden' is 'type=text'. I don't know of an admin switch that will do that, so maybe a mod you've installed ?