Is Sarge a mix of testing/unstable really?

[Thierry <Thierry@echotech.ch>]

Hello,

I've always believed that "sarge"=="testing" .
As I want to follow sarge for my new servers up to the point where it's 
"sarge"=="stable" and stick with it afterwards, I've put the following 
in my /etc/apt/apt.conf :
APT::Default-Release "testing";

Now, if I run 'apt-get dist-upgrade -s' I'll see a bunch of packages 
coming out of testing.
Interestingly I tried out to change the apt.conf into:
APT::Default-Release "sarge";

Issuing an apt-get dist-upgrade -s spits out a *different* list of 
package than the previous one coming from unstable !
(Note that I'm always using "-s" first to check first what pain I'm 
going to inflict to the machine...)

Can anyone explain this behaviour, if this is expected, and if I totally 
misunderstood anything? :-)

Cheers
Thierry

Some of the messages to illustrate what I mean:
1: with APT::Default-Release "testing";
[...]
Inst linux-kernel-headers [2.5.999-test7-bk-9] (2.5.999-test7-bk-16 
Debian:testing)
Inst libc6-dev [2.3.2.ds1-10] (2.3.2.ds1-18 Debian:testing) []
Inst perl-modules [5.8.2-2] (5.8.4-3 Debian:testing) []
[...]

2: with APT::Default-Release "sarge";
Inst linux-kernel-headers [2.5.999-test7-bk-9] (2.5.999-test7-bk-17 
Debian:unstable)
Inst libc6-dev [2.3.2.ds1-10] (2.3.2.ds1-19 Debian:unstable) []
Inst perl-modules [5.8.2-2] (5.8.4-5 Debian:unstable) []