I appended an example file where i have four bones. The bone "pivot2" has two pivot constraints and should rotate around the left or right bone depending on it's own rotation. If you rotate "pivot2" then you should see how it should look like. But if i rotate the parent "pivot1" then "pivot2" starts moving without being rotated. I don't know if it is intended to be relative to the parent space or the bone himself, but either way the result is wrong and unusable.