We changed how the frequencies are calculated for major and minor ticks in version 2.8 of shinobicharts.
Pre-version 2.8, if there wasn't enough space for the desired majorTickFrequency, we would continue to multiply the value by 2 until there was enough space for the tick labels (10, 20, 40, e.t.c).
Now however, if there is not enough space for tick labels at your desired tick frequency, the chart automatically calculates a frequency that will fit along the axis. In your case, a major frequency of 10 will cause tick labels to overlap, the chart then falls back to a tick frequency of 50.
To workaround this, you should be able to set your majorTickFrequency to something slightly higher, e.g. 20, although the required value depends on the height of your chart. You could also take a look at the sChart:majorTickValuesForAxis: datasource method.
It was a bit of an oversight on our part to change the old behaviour without adding a way to get it back. However, we are planning on making this more customisable in the near future - I'll make sure we update this ticket when it's released.