debconf-set-selections + dpkg-reconfigure: why don't my settings stick?

[Alexis Huxley <ahuxley@gmx.net>]

I would like to configure some packages "the Debian way", but
non-interactively,

I used debconf-set-selections to set the settings I wanted.
Then I used debconf-get-selections to verify that the setting had
been correctly registered.

Finally I ran dpkg-reconfigure in non-interactive mode on the packages
expecting that the just-set settings would be applied, but in all
cases I get the previous setting being applied, i.e. as if I had not
run debconf-set-selections at all.

Am I missing some step here?

Here's an example:

nidi# echo -e "tzdata tzdata/Areas select Europe\ntzdata tzdata/Zones/Europe select London" | debconf-set-selections
nidi# debconf-get-selections | grep tzdata
tzdata  tzdata/Zones/Australia  select
tzdata  tzdata/Zones/Asia       select
tzdata  tzdata/Zones/Etc        select  UTC
tzdata  tzdata/Zones/SystemV    select
tzdata  tzdata/Zones/Africa     select
tzdata  tzdata/Zones/America    select
tzdata  tzdata/Zones/Arctic     select
tzdata  tzdata/Zones/Pacific    select
tzdata  tzdata/Areas    select   Europe
tzdata  tzdata/Zones/Antarctica select
tzdata  tzdata/Zones/Atlantic   select
tzdata  tzdata/Zones/Europe     select  London
tzdata  tzdata/Zones/Indian     select
nidi#

It now looks like the setting I want, but when I reconfigure:

nidi# dpkg-reconfigure -f noninteractive tzdata

Current default timezone: 'Etc/UTC'
Local time is now:      Fri Oct  5 22:31:17 UTC 2007.
Universal Time is now:  Fri Oct  5 22:31:17 UTC 2007.

nidi#

I poked around in the postinstall script of the packages I tried
(tzdata and locales) and I think that the script puts the actual
setting in effect (e.g. as defined by /etc/timezone or /etc/locale.gen
depending on the package) at a *higher* priority than the value in
the debconf database.

I can understand this: if someone does things in the traditional
edit-the-config-files way, then that setting is not reset by
using dpkg-reconfigure etc.

But nevertheless, it should be possible to have dpkg-reconfigure
apply the setting I've seeded its db with? Is there nothing like

dpkg-reconfigure --settings-in-debconf-db-get-higher-priority-than-values-found-in-the-field

?

Any advice appreciated!

Alexis