Chrome not handling jquery ajax query

I have the following query in jquery. It is reading the "publish" address of an Nginx subscribe/publish pair set up using Nginx's long polling module.

function requestNextBroadcast() {
        // never stops - every reply triggers next. 
        // and silent errors restart via long timeout. 
        getxhr = $.ajax({
            url: "/activity",
            // dataType: 'json',
            data: "id="+channel,
            timeout: 46000, // must be longer than max heartbeat to only trigger after silent error. 
            error: function(jqXHR, textStatus, errorThrown) {
                alert("Background failed "+textStatus);  // should never happen 
                getxhr.abort(); 
                requestNextBroadcast();  // try again
            },
            success: function(reply, textStatus, jqXHR) {
                handleRequest(reply);   // this is the normal result. 
                requestNextBroadcast(); 
            }
        });
    }

The code is part of a chat room. Every message sent is replied to with a null rply (with 200/OK) reply, but the data is published. This is the code to read the subscribe address as the data comes back.

Using a timeout all people in the chatroom are sending a simple message every 30 to 40 seconds, even if they don't type anything, so there is pleanty of data for this code to read - at least 2 and possibly more messages per 40 seconds.

The code is 100% rock solid in EI and Firefox. But one read in about 5 fails in Chrome.

When Chrome fails it is with the 46 seconds timeout.

The log shows one /activity network request outstanding at any one time.

I've been crawling over this code for 3 days now, trying various idea. And every time IE and Firefox work fine and Chrome fails.

One suggestion I have seen is to make the call syncronous - but that is clearly impossible because it would lock up te user interface for too long.

Edit -