Field permissions and private fields don't work well for types of entities that don't have an "author"

For entities that do not have any author information stored (i.e., no $object->uid property), the behavior of Field Permissions can be a little weird.

For example, if you attach a field to a taxonomy term and set it to be a private field, regular users who have access to create taxonomy terms will never be able to add values for that field (since they don't "own" the term). Similarly, if you give someone only "edit own value for field X" permission for that field, they will not ever be able to edit it when editing the taxonomy term, since neither they nor anyone else "owns" the taxonomy term.

This all mostly works well for fields attached to nodes and users (which are the most important use cases anyway). But it should be made to work better for others, and there might be some things we could do.

For example, maybe fields that have been configured to be "private" should always grant edit access on object creation, without bothering to check the owner...