gdal vector convert, should --output-layer be required with CSV?

src.csv and dst.csv are identical, containing:

lon,lat,desc
-123,90,"some other stuff"

then run:
gdal vector convert -i src.csv -o dst.csv --append

ERROR 1: Attempt to create csv layer (file) against a non-directory 
datasource.
ERROR 1: Failed to write layer 'src'. Use --skip-errors to ignore errors 
and continue writing.

but the following works:
gdal vector convert -i src.csv -o dst.csv --append --output-layer dst

Should --output-layer be required with CSV?

The same happens if source is a single layer .gpkg.

Thanks!
Scott


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