Long lines trigger "Excessive signature"?

[Otto J. Makela]

This is under Fedora release 40 (Forty), with GNU Emacs 29.4
(build 1, x86_64-redhat-linux-gnu, X toolkit, cairo version 1.18.0,
Xaw3d scroll bars) of 2024-07-16 and Gnus v5.13, posting via
eternal-september.org

When sending a message with lines longer than 79 charactes (like an URL),
I am correctly prompted by gnus with

        You have lines longer than 79 characters.  Really post? (y or n)

but accepting this with y, if the message includes my normal automatically
included 4-line signature (below, which I've used since 2010), gnus reject
the posting with

        Denied posting -- Excessive signature.

This 4-line signature will be acceptable to gnus if I don't have long lines
in my message, nor does a signature of 3 lines seem to trigger the issue.
It seems to be a matter lines, not the character count of the signature.

How should one go about debugging this?

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