bug#50842: 28.0.50; problem with fill-paragraph

["Peter Münster" <pm@a16n.net>]

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Hello,

When using M-q (fill-paragraph) in message-mode with latest version from
git-master, the result is not as I would expect.

Example buffer:

--8<---------------cut here---------------start------------->8---
From: xxx
To: xxx
Subject: xxx
--text follows this line--
You wrote:

> bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla        
>           bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla      
>           bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla      
--8<---------------cut here---------------end--------------->8---

When typing M-q in the quoted text, I get this:

--8<---------------cut here---------------start------------->8---
> bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla
bla bla bla > bla bla bla bla bla bla bla bla bla bla bla bla bla bla
bla bla bla bla > bla bla bla bla bla bla bla bla bla bla bla bla bla
bla bla bla bla bla
--8<---------------cut here---------------end--------------->8---

But I would like to get this (as with Emacs-27.2):

--8<---------------cut here---------------start------------->8---
> bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla
> bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla
> bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla
> bla bla bla bla bla
--8<---------------cut here---------------end--------------->8---

How could I get back the behaviour of Emacs-27.2 please?

TIA for any hints,
-- 
           Peter

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