dpkg-reconfigure debconf sets files in /var/cache/debconf whosemodes
(permitions) are not as configured in /etc/debconf.conf. I guess it is
also because of the umask setting.

How to reproduce?
1. Set the mode of config at /etc/debconf.conf to 0644.
2. Manually chmod /var/cache/debconf/config.dat to 0644, just to be sure.
3. Set root umsak for something restrictive, such as 0077.
4. Run dpkg-reconfigure debconf.
5. Compare /var/cache/debconf/config*.dat actual value to the mode from
   /etc/debconf.conf.
6. Now repeat the procedure while setting root's umask at step 3 for
   something less restrictive, such as 0022.