@atom,
It seems like you have missed out updating stripLine values. Adding the following lines should work fine in your case.
chart.axisX[0].stripLines[0].set("value", chart.axisX[0].get("viewportMaximum"));
chart.axisY[0].stripLines[0].set("value", chart.axisY[0].get("viewportMaximum"));
—-
Manoj Mohan
Team CanvasJS