Example code:

var js = JSON.stringify({ note: 'questions?? more information' });
$.ajax({
    data: js,
    dataType: "json",
    success: function (data) { }
    error: function (XMLHttpRequest, textStatus, errorThrown) { }
});

I believe that the issue lies in ajaxPrefilter. The jsre is too aggressive and matches the first '??' it finds anywhere in the data string. The '??' gets replaced w/ an anonymous callback function name, such that the server receives the note field as:

    questionsjQuery<anonymous numbering> more information

On return from the server, the ajax call cannot find the anonymous function and goes straight to the error handling instead of calling the success function.