Grid data disappears after adding a row (using IE)

Taking quickref/grid.htm and then adding the following after "document.write(obj);"

var newRow = ["WG","Will Gibson", "999,999.00", "99,000.00", "900"];
    
newData = myData;
newData.push(newRow);
obj.setCellText(newData);
    
obj.setRowCount(21);
obj.refresh();

i.e. adding an extra row to the 2-D javascript array data and then loading this new dataset into the grid and refreshing, causes the data to disappear from the grid in IE, whereas in FF the new row is displayed OK as the bottom row of the refreshed grid.

Any ideas what might be going on here?

Thanks
Will