When you create a new key in kleopatra, the only instruction shown is "Please enter the passphrase to
protect your new key". If you enter a passphrase shorter than 9 characters, you only get a warning and
"A passphrase should be at least 9 characters long. A passphrase may not be a known term or match certain pattern."
after you have clicked "OK" in the new pinentry window for the second try.
I would at least expect a short note "(>= 9 characters)" in the first pinentry window.
And add that information in the warning that appears if you try an empty password, too.
(Instead of just "An empty passphrase is not allowed.")