.ods files in Calc: How do I keep cell borders from disappearing after saving and closing?

In Calc, I’ve created a brand new .ods file and have entered plain text, with borders on some cells. After saving, closing and re-opening, my single line borders are still there, but no other borders eg. my double line borders disappear every time. How do I prevent this from happening?

This bug seems to have been around for some time. Reported on Bug 79260. It only affects the double line borders.

Thank you! I sincerely appreciate your answer. Pity for us accountants (needing the double line), but at least I know I can use alternative borders.