posting JSON via AJAX results in garbled request payload

I'm attempting to post JSON data to the server and use the JSON in the response to ultimately populate the datatable. However I've experiencing some strange behavior.

Using this code:

table_config.ajax = {
                "type": "POST",
                "url": $(location).attr('pathname'),
                "data": JSON.stringify({'member_id':2444}),
                "dataType": "json",
                "contentType": "application/json",
                "dataSrc": "results.data"
            };

I get a 400 HTTP response and the request payload looks like:

0=%7B&1=%22&2=m&3=e&4=m&5=b&6=e&7=r&8=_&9=i&10=d&11=%22&12=%3A&13=2&14=4&15=4&16=4&17=%7D

What's going on here?