Everything else works great - I'll try your workaround for a while as I can't find any other app to stick with. (MailDroid seems just okay, not fabulous). Can't belive Google managed to totally mangle the email app, which IMHO is only second in importance to the telephone.
ETA: Scudder, I did figure out part of it - K9 says I have 7 emails in my GMail account inbox, but I had deleted all but one (so count should show 1). I logged in online and I do indeed have 7 emails in my inbox. They weren't loading into K9, even with a manual refresh.
I don't have a solution for this - yet. I wish they had some kind of online instruction.
ETA: There is a setting (Account > Account Settings > Fetching Mail > When I delete a message...) to delete on phone/not on server or also delete on server. Not sure if it will solve the issue yet.