Comment # 6 on bug 1217414 from Boehmer

Maybe it's not really dangerous. But is at least very confusing behavior.
It was also reported as a bug once (Bug 606249) and has been fixed.

There is also a crucial difference between Leap 15.5 and Tumbleweed:

In Leap, the value 'Umask for Home Directory' only sets the permissions for the
home directory. The umask for new logins is unchanged (022). - This is what I
expect and the help text also describes.

In Tumbleweed, the value 'Umask for Home Directory' sets the permissions for
the home directory of the newly created user AND the umask for all new logins
(of all users). This changes the system behavior for all other users (including
root) if the umask is not explicitly set in the profile or elsewhere. The
standard configuration (profile, bashrc ..) does not set the UMASK. (See also
https://en.opensuse.org/SDB:Set_UMASK)

If you look at the configuration files in Tumbleweed, you will see that there
is no file '/etc/login.defs'. There is only '/usr/etc/login.defs'. It seems
that the PAM module reads the default umask directly from the file
'/etc/login.defs.d/70-yast.defs' if '/etc/login.defs' does not exist.

Why isn't the 'Umask for Home Directory' saved as the HOME_MODE variable?

man login.defs
...
HOME_MODE (number)
            The mode for new home directories. If not specified, the UMASK is
used to create the mode.