Many thanks for all the replies.
@Sidney, that helps clarify File.Select vs File.decoder.
@jessta, knowing there is (was) a bug makes me feel better 
@christian, brilliant, I’ll upgrade and try again…
It works! In both Chromium and Firefox on Ubuntu 
— it might need some automated tests to ensure it works every time.
I upgraded the File package using @jerith’s upgrade approach.
@kwindow, I guess from your task comment you too would very much appreciate a tutorial article on Tasks 
@dmy, that’s how I did it, good to have the confirmation. Thanks also for the Cmd.batch and List.map pointers.