I have a SafeCracker form that will allow users to enter data about a trip. Users will not necessarily be logged in when submitting the form. For that I have set up a "Guest Posters" member group. That group contains a single "Guest Poster" user. That user's member_id is used for the logged_out_member_id parameter in SafeCracker.
That part all works fine.
Things fall apart when a user wants to edit a form submitted by somebody else. This can happen if, for example, an admin starts the form for a user and then hands it off to the user to complete the rest. In that scenario, if the user submits the form he sees the error: "You are not authorized to perform this action".
The error message originates because can_edit_other_entries ("Can edit entries authored by others" in the control panel) is set to 'n' for logged out users. But since I have that value set to 'y' for the "Guest Posters" group, I would expect the form submission to succeed.
I've stared at this for too long. At this point I figure there are two possibilities: either the solution is obvious and Friday fatigue has blinded me; or this is a bug in EE.