[jQuery] possible bug when parsing xml on IE7?

[MacFly!]

Hello,
First, I use the latest version of JQuery : 1.2.6
I try to get elements from xml returned by an ajax call.
It's works fine with FF2 but not with IE7.
here is my simple code :

$.ajax({             type: "POST",
                        url: "myURL.do",
                        data: "&hidden=getValue,
                        dataType:"text/xml",
                        success: function(xml)
                        {
                                alert($(xml).find("el").size());
                        },
                        error: function(error){alert("error");}
           });

and my xml returned from the server is :

<?xml version="1.0" encoding="utf-8"?> <node><leaf><field>ST_ID</
field><patterns><el>TO</el><el>DA</el></patterns></leaf></node>

size = 2 in FF2 and 0 in IE7
Don't know where the problem comes from, I try also  with "//el", $
("el",xml).each...but no success.
Can someone help me with that?

Thanks for your help in advance