Module automatically changes category permissions to wrong values

I'm using the following category structure:

  dogs
    -- all animals
  cats
    -- all animals
  horses
    -- all animals

where "all animals" is a single category with multiple parents. The reason is that there are some postings that only apply for dogs, cats, horses and some for all animals. This structure avoids to allow multiple categories for a posting (the user just chooses "all animals").

PROBLEM: If I try to modify the access permission using taxonomy_access the settings for "all animals" will be set automatically to ALLOW everything (view, change, delete, create). Even if I remove all permissions it will change back without ticking any box.

Reproduce:

1. Open category permissions for anonymous user.
2. Tick all boxes for one vocabluary (cats, dogs, horses, multiple all animals).
3. Set everything to remove.
4. Save
5. Open category permissions for anonymous user again: all boxes unticked (as expected)
6. Save again (not changing anything)
7. Open category permissions for anonymous user again
8. all "all animals" lines are set to allow everything.

I'm using

Drupal 4.6.1
taxonomy_access 4.6.0 (+ latest security patch)
Apache 2
PHP 5

Chris