Calc backup files all zero KBs

Why are my calc backup files all zero KBs?

There are also dozens of backup files for a particular time. There is only supposed to be one every 10 minutes. Very odd.

It happens with all version of calc that I have run.

Are the document(s) password-protected and non-ODF? I suspect tdf#118639

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@ Mike Kaganski

Yes, the document(s) are password-protected and non-ODF. Looks like tdf#118639