apt_preferences: how to get cogito from unstable?

[Martin Wilck <Martin.Wilck@particle-dynamics.de>]

Hello,

I'm a long-time Linux user now experimenting with Debian for the first
time. I have a problem setting up apt package preferences. 

I am using sarge with this apt.conf:
APT::Default-Release "stable";

I have configured testing/unstable as additional sources in
sources.list. My /etc/apt/preferences file looks like this:

Explanation: Keep unstable priority below installed 
Package: *
Pin: release a=unstable
Pin-Priority: 80

I came across bug 317914 which prevented me from unpacking Linus' kernel
tree, and I thought it might be a good idea to add a preferences rule
like this:

Package: cogito
Pin: version 0.11.3*
Pin-Priority: -10

To my understanding, "apt-get remove cogito; apt-get install cogito"
with these settings should install version 0.12.1 from unstable instead
of the broken testing version 0.11.3+20050610-1.

However, I am still getting 0.11.3. I have tried many other variations
(assigning high priority to 0.12.x, changing the rule order, using Pin:
release instead of Pin: version, ...), but always with the same outcome.
So I ended up doing simply "apt-get -t unstable install cogito", but I'm
mnot satisfied with that solution. I'd like to understand why I couldn't
get the preferences to work as desired.

The idea is "In general I give low priority to unstable; but I don't
like version X of package Y in testing and would rather use the unstable
version of that package". How can this be cast into /etc/apt/preferences
syntax?

Regards and thanks,
Martin