Calc dumps format changes

I am using LibreOffice on a Macbook Pro running OS X 10.10.5 (Yosemite).

I have data already in a spreadsheet. I set the header row format to NOT automatically wrap text, and then I set the column widths. I save, and close the spreadsheet and log out of LibreOffice.

When I re-open the spreadsheet, the column widths are all wrong (but not to any reasonable setting that makes sense to me), and the header row format has gone back to automatically wrap text.

How can I get LibreOffice to save the format changes I make, and stop re-setting them? (And why is it doing this anyway?)

Thank you.

What format do you use to save spreadsheet?