Number of Columns does not change

Sorry for putting this in General, but I did not want to put it in bug reports, since it's rather a lack of my understanding of datatables than a bug.
I am building a table that shows different data inputs. They all have a different content and a different number of columns. I am using an ajax call to get the data from the server. It would be great if the datatable could adjust to the number of columns. So far I have managed to update the content, but the number of columns seems to stay fixed from the first data call. I have played around with the b-options and this combination seems to be the best working one for me. The debugger returns "iquqak".
Table definition:

<table id="foobar" cellpadding="0" cellspacing="0" border="0" class="table table-striped table-bordered table-condensed"></table>

Ajax Call:

var oTable = null;
$.ajax({
    url: config.renderURL + "/" + id,
    success: function(json) {
	data = json;
	if (oTable !== null) {
		oTable.fnClearTable();
		oTable.fnAddData(json.aaData);
	} else {
		oTable = $('#foobar').dataTable({
			"iDisplayLength": -1,
			"bDestroy": true,
			"bSort": false,
			"bRetrieve": true,
			"aaData": json.aaData,
			"aoColumns": json.aoColumns
		});
	}
	oTable.fnDraw();
    error: function(xhr, err) {
	alert("No content found");
    }
});

For example if I use this json for the first call, it works fine:

{"iTotalRecords": "4", 
"aoColumns": [
{"sTitle": "", "sDefaultContent": "", "mDataProp": null}, 
{"sTitle": "Column 1", "sDefaultContent": "", "mDataProp": null}, 
{"sTitle": "Column 2", "sDefaultContent": "", "mDataProp": null}, 
{"sTitle": "Column 3", "sDefaultContent": "", "mDataProp": null}], 
"aaData": [
["Row 1", "1", "2", "2"], 
["Row 2", "1", "2", "3"], 
["Row 3", "45", "5", "6"], 
["Row 4", "6", "6", "7"]], 
"iTotalDisplayRecords": "4", 
"sEcho": "0"}

If I want to load a table with more than 4 columns it will still only show 4.