Ref T7703. See that task and inline for a bunch of discussion.
Briefly, when we run implicit policy rules ("to see a revision, you must also be able to see its repository") at query time, they don't apply to other viewers we might check later.
We do this very rarely, but when we do we're often doing it for a bunch of different viewers (for example, in Herald) so I don't want to just reload the object a million times.