On a X-Y scatter chart with the linear regression line statistic enabled, the
line properties are not saved. One can change the thickness, style, and color.
The changes are made to the chart. However, after saving and closing the
document, the changes are not kept. Upon reopening the document, the properties
of the regression line statistic are reset to the defaults. Thus any
customization of statistic line attritubes have to been re-done each time the
document is opened.