Libre-Office Calc - Default setting choices

Using Libre-Office Calc - the spread sheet, I have my data series and its line on the graph…
After right mouse click on chart wall and choosing edit from drop down menu
I double click the line to format it…

the window appears with two tabs one for Options and one for Line
choosing the Line tab the various properties appear
along side Thickness is a DEFAULT value 0.07cm
I wish to reduce this to 0.04…

Which I do and its changes on the screen…
BUT every time I resave the spreadsheet and reload it, the line is at the default value of 0.07cm again… it will not keep the new replaced value… no matter what value I choose and save, the spreadsheet comes back with the line thickness value of 0.07, I assume is the default value…
possible bug maybe I don’t know…

SO…
my question is…
Can I reset the default value somewhere in options or customize instead?

this is most annoying, I’m surprised the software designers chose 0.07cm in the first place the line is far to thick…
thank you