I agree that this is something that the chart should do automatically. We will evaluate if there are any hidden issues in other scenarios or if it can be safely enabled as a default.
In the meantime, you can use this line to scroll the chart back to the first column keeping the current drilldown:
chart.setPie(chart.getPie(), 0);
See http://jsfiddle.net/49kqbty8/
It does sometimes slightly change the width of the columns but that usually happens if there were only a few large columns being visible before.