line charts can extend over their axes and go into the invisible area beyond the chart. This is especially noticeable with floating point numbers < 10. It's caused by bad rounding in Ext.chart.axis.Axis.calcEnds.
I changed the code to:
out = Ext.draw.Draw.snapEnds(min, (max >> 0) + 1, me.steps);
and after this my starts don't get chopped off at the chart's border anymore