JQuery Ajax post parameters sometimes not sent on IE

The problem I am having is that when I use jquery ajax post, with very low frequency (< 2%), the post parameters never make it to the server. I do see the post request in the access log. It seems to happen only on IE (I've observed it on 7, 8, and 9 in the logs).

When I switch the call from type "post" to type "get" the issue goes away.

Has anyone else ever seen this odd behavior on IE? Thanks!

I have seen this for various ajax calls, but here is a typical one:

var data= {
    "guess" : "m1",
    "eas" : "hello world"
};

$.ajax({
    url: "http://myco.com/ajaxcall.action",
    data: data,
    type : 'post',
    dataType: 'json',
    success: function(data) {},
    error: function() {}
});

Update: passing "cache: false" does not fix the issue.