Total system lockup when copying rows to clipboard in Calc

Using LibreOffice on Windows 10 64-bit.
In a humdrum spreadsheet, I selected around 350 rows, did Ctrl+C.
First the app locks up – it seems to be crunching hard doing that copy. Subsequently, the whole system locks up. I can’t even Ctrl-Alt-Del out of it. I have to do a hard shutdown.

It appears somebody else reported a lockup due to AutoSave. Maybe an autosave is happening in the midst of this copy-to-clipboard function?