On my debian/sid install,

dev@lal:~$ su -
Mot de passe :
root@lal:~# umask
0002

I expected 022 (or 0022, I don't know what the fourth 0 is).

I checked /home/dev/.profile, .bashrc, and likewise in /root/,
/etc/profile, /etc/profile.d, /etc/bash.bashrc, in fact the whole /etc directory.

The closest already existing bug report I could find was:
#1112678 login.defs: USERGROUPS_ENAB and UMASK are nonfunctional

Jérémy