Join version 8.5 - and I didn't really see any useful information in the man file explaining any different formats for the -o option.

Omitting the "-o auto" gets rid of the error, but produces a file that's not so helpful.

All the lines from the "all" file are still there in the output (which I redirected to a new file). None have been replaced by the corresponding matches from the source file and they have all had a space prepended to them.

The lines from the source appear in the file without the first field, so they start with a comma, and are placed immediately after the lines they should have replaced.

I can probably make a macro in TextPad (in Windows) to correct this.