JFFS2 bind mount bug ?

[Joakim Tjernlund]

Got two JFFS2 partitions (on / and /var) and do
  PWROOT=/var/os
  mount --bind "${PWROOT}"/etc/shadow /etc/shadow
then I modify "${PWROOT}"/etc/shadow and expect both "${PWROOT}"/etc/shadow /etc/shadow to
be equal but the /etc/shadow is unchanged!
Kernel here is 5.15.129

Doing the same on my 6.1.54-x86_64 works which uses XFS/tmpfs works

 Joakim