Description: After applying double border lines to some cells in .ods format, then "Save As" .xlsx format, the double cell border lines get replaced by single border lines after closing and opening the .xlsx document again. Steps to Reproduce: 1. Create Libre Calc document and save it as .ods format. 2. Add double border lines to any cell 3. Click "Save As" and save it as .xlsx format 4. Close document 5. Open .xlsx document 6. Double border lines are changed to single Actual Results: After saving it in another format, closing and returning to the document with the new format, the double border lines are replaced with single border lines. Expected Results: After saving it in another format, closing and returning to the document with the new format, the double border lines should remain where I applied them. Reproducible: Always User Profile Reset: No OpenGL enabled: Yes Additional Info: Version: 7.3.2.2 / LibreOffice Community Build ID: 30(Build:2) CPU threads: 2; OS: Linux 5.17; UI render: default; VCL: gtk3 Locale: en-US (en_US.UTF-8); UI: en-US 7.3.2-1 Calc: threaded