Alan has a great write-up about assembly binding policy. I'll copy a paragraph to avoid duplicate discussion:
<quote> Fusion offers a rich (albeit complex) binding policy system that allows various parties to influence assembly binding behaviour by authoring XML configuration files that can redirect a reference to one version of an assembly to another. The three primary forms of binding policy are: application policy, publisher policy, and administrator (or machine) policy. Given a strongly-named assembly reference, these policy files are consulted in order (app, publisher, machine) to arrive at a final post-policy reference which Fusion will try to bind. The output of evaluation of each policy stage is used as input to the next policy stage until the post-policy reference is obtained. </quote>
Unfortunately the chaining of binding policy means if you are in the later stage (Like admin policy) of the policy evaluation, your binding redirect may be bypassed by policy evaluation in earlier stage.
If you don't want this to happen, please include a range in your binding redirect statement. I.e. <bindingRedirect oldVersion=”0.0.0.0-9.65535.65535.65535”, newVersion=”10.0.0.0”/>