jquery selector problems with <table> directly within <tr>

by benny

HTML

<html>
    <body>
        <p id="a"></p>
        <p id="b"></p>
        <p id="c"></p>
        <p id="d"></p>
    </body>
</html>

JavaScript

var invalidhtml = '<tr><form action="" method="post"><table><tr><td></td></tr></table></form></tr>';        

var validhtml = '<tr><form action="" method="post"></form></tr>';        

var validhtml2 = '<table><tr><td><form action="" method="post"><table><tr><td></td></tr></table></form></td></tr></table>';        

var validhtml3 = '<tr><td><form action="" method="post"><table><tr><td></td></tr></table></form></td></tr>';        

var form = $("form", validhtml);
$("#a").html(form.attr("id"));
form = $("form", validhtml2);
$("#b").html(form.attr("id"));
form = $("form", validhtml3);
$("#c").html(form.attr("id"));
form = $("form", invalidhtml); // crash here
$("#d").html(form.attr("id"));