JQuery :: Switched To 1.6.1 Immediately The Success Callbacks Of Functions Did Not Trigger?

There is probably something going on in my environment but when running 1.5.2, jquery runs and behaves fine. When I switched to 1.6.1 immediately the success callbacks of ajax functions did not trigger. I did not see the release notes mention anything new regarding that.
This includes

$.post("url", function() { console.log("will i get printed?"); });

Here is a code sample which fails

$(".foo").click(function(e) {
var link = $(this);
e.preventDefault();[code].....

The callback function for the ajax is never invoked.As part of my application, I have the following ajax setup going

$.ajaxSetup({
'beforeSend': function(xhr) {xhr.setRequestHeader("Accept", "text/javascript")}
});

Firefox 4.0.1, Ubuntu 10.04, Firebug 1.7