X-axis tickInterval not working correctly in highstock chart

I show a series of series in the height table. I chose highstock because I want to show at least 4 hours of data with scrollability if the user adds data points in these 4 hours (but I don’t want RangeSelector or the navigator to be turned on if this relates to the problem I have )

I thought it would be easy, but I am having problems with 15 minute intervals along the x axis. When one data point is dynamically added, the graph correctly shows the time intervals of 15 minutes, but when more data points are added, the x axis starts to incorrectly scale the time. If I then refresh the page and display a graph with several data points, I get really weird tickIntervals.

Here are my xAxis options:

xAxis: {
        type: 'datetime',
        min: 1361815200000,
        max: 1361829780000,
        tickInterval: 15 * 60 * 1000,
        minTickInterval: 15 * 60 * 1000, // 15 minute intervals
        gridLineWidth: 2,
        labels: {
            formatter: function () {
                var d = new Date(this.value);
                return (d.getMinutes() == 0) ? '<b>' + Highcharts.dateFormat('%H:%M', this.value) + '</b>' : d.getMinutes();
            }
        }
    }

: http://jsfiddle.net/pxCsX/

? minRange, type xAxis series highstock, bupkis.