apt-get upgrade confusion.

[Rolf <rolf@ses.tas.gov.au>]

Hello
Just when I thought I had my head around the apt-get mechanism when dealing 
with a mixing of stable and testing (and unstable) packages, this problem 
turns up.

Sources list contains stable and testing and unstable references. 
/etc/apt/preferences contains 3 pins:

Package: *
Pin: release o=Debian,a=stable
Pin-Priority: 900

Package: *
Pin: release o=Debian,a=testing
Pin-Priority: 400

Package: *
Pin: release o=Debian,a=unstable
Pin-Priority: 50

if I do an apt-get update everything goes smoothly, if then an apt-get 
upgrade, a miscellaneous bunch of packages want to get upgraded to the 
testing version.

The only logical answer is that some package install I have done requires 
these updated versions and so it is wanting to it.

But the system is working fine, the only packages I've recently added work 
fine, apt-get check reports no problems. apt-cache policy package-name says 
sensible things.

If it is the case that these package versions are required due to some 
other dependency or relationship, how do I find out what that is?

If not (a) how can I find out why it wants to do this and (b) how do I stop 
it, unless it is recommended that I let it do it?

Many thanks.

rolf.