how to make pivot chart modification to stay after refresh chart

[tng]

i created a pivot table for using the pivot chart options. I created the
chart. after i modified the line type and hit the refresh button in the tool
bar, the chart line type change to a system default settings. all the
changes i made to the chart is gone.

is there any way i can make the changes stay in the chart after the refresh
the chart.

thanks in advance

thomas