PMS is pretty vague on sandbox. It mentions 'permitted read list', 'permitted read list', 'predict list' and 'deny list'. However, as far as I can see, there's no explanation in what order those lists are applied and what are the default contents of those lists.
When we wrote that section, sandbox didn't really have a stable API, and we had to keep changing configuration to keep up with changes. I dunno if the situation has improved.
the base behavior has never really changed. it's been that way for the better part of a decade.
I'm kinda repeating myself but #631722 has a more complete description of what needs to be noted. *** This bug has been marked as a duplicate of bug 631722 ***