/etc/apt/preferences Confusion

[Dave Steinberg <dave@taro.homeip.net>]

I have been tracking testing for the longest time, but I would like to be
able to get up-to-date mozilla and galeon packages from unstable.

As I understand it, /etc/apt/preferences can help me with this.  I can add
entries for both releases in sources.list, and then set priorities to
keep packages that I've installed from unstable up to date, while using
testing as the source for other packages.

I think that all I need is this:

Package: *
Pin: release a=unstable
Pin-Priority: 101

The idea here is that, testing gets an automatic priority of 989.  If any
package could be upgraded to either a testing or an unstable version,
testing will win.  If a package version is already higher than the testing
version, the unstable version will win (unless unstable is below 100 or
testing is 1000 or higher).

Is this correct?  The reason that I ask is, having done this, when I try
apt-get update && apt-get upgrade, it wants to update a number of
packages, like binutils, gimp1.2, groff, klogd, and perl, to unstable
versions.  Any ideas why this might be?  Have I misunderstood how
priorities work?

Any insights would be appreciated.

-- 
Dave Steinberg
dave@taro.homeip.net