In the meantime, this can be done with the following form.
<form method="get" action="index.php?" onsubmit="return(this, 'index.php?');"><input type="hidden" name="page" value="item"><input type="hidden" name="id" value="Search">Listing ID: <input size="5" type="text" name="id"><input type="submit" value="Search" class="button"></form>