It is bad form, pretty much anywhere, though, to have a message body with no content. Even if the subject is "the complete question," it's always a good idea to say something like, "The subject says it all."
I have no idea what group that was, as I doubt the owner of either the JAWS for Windows group or Windows 10 for Screen Reader Users group would have this reaction. The most frequent problem I see is not that the subject line is too long, or too specific, but that it's generic, e.g., "I need help," and giving the reader absolutely no idea about what.
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Brian - Windows 10 Pro, 64-Bit, Version 2004, Build 19041
Always remember that computers are just glorified light bulbs - they rarely fail in continuous use and usually go pop when turned off and on.
~ Technician with the username Computer Bloke, on Technibble.com