Trend line equation formatting not saved

Working in V 6.1.5 on Windows 8.1, I have data plotted and a trend line calculated. I format the trend line and save the file, but upon reopening the file the formatting has been lost.

How can I save the formatting of the trend line?

Thank you.

In what format are you saving the file? Always use the LibO native formats: for Calc, .ods

Yes, that worked. Thank you!