If that's not easily fixable, perhaps I'll submit a patch to the paredit
project so that they stop relying on lisp-paragraph-fill [0] and instead
use the default (which is fill-paragraph).  That's how I came to notice
this behavior change in GNU Guix, which is written in Scheme; using
scheme-mode doesn't exhibit the issue since it's just using
fill-paragraph.

[0]  https://paredit.org/cgit/paredit/tree/paredit.el#n1066

-- 
Thanks,
Maxim