I got a puzzle problem with safari which version is 5.1.2.

this is my code:
$.ajax({
type:"POST",
url:"login_auth.jsn",
dataType:"json",
data:{'_ajax':1,'_web_cmd':'cmd login '+username+' '+pwd + '\r\n'},
success:function(returnedData){
alert("get response");
alert("ctx:"+ returnedData);
if(returnedData.status=="ok")
{
save_language(lang, username);
}else{
alert(infomsg.login_false);
window.location.href="index.jsp";
}
}
});

After execute this ajax in safari, the "returnedData" is null. But in FF, chrome and IE7~IE9, the "returnedData" is a json object and the code work correctly.

The 2nd alert is "ctx:null"
Use develop tool in safari, the console err is "TypeError: 'null' is not an object (evaluating 'returnedData.status')";

Anyone got the same problem?