I've encountered some puzzling behavior related to
https://debbugs.gnu.org/cgi/bugreport.cgi?bug=48170.

Specifically, running under emacs -Q commit
d6dc66053d846b6fc041889b4d0f383c8dac4da3 of 2021-05-30 on GNOME, if I load
up https://github.com/raxod502/bug48170-repro, then `next-line' navigates 1
line down, but `previous-line' navigates 2 lines up!

Any ideas about what might be causing that?

Best,
Radon