How do I save a cwk document after opening with libre. when I reopen the original cwk document it is blank

[Hendo]

When I reopen same cwk document it is blank

[erAck]

I didn’t know one could also save to .cwk and I doubt that’s intentional (hence the blank document). However, best is to save to .ods for Calc spreadsheets or .odt for Writer text documents.