Reproduction steps

1. Have a user who can see hidden pages
2. Create a book
3. Create a version "v1"
4. Create a variant "A" and a variant "B", don't change any settings for them
5. Create a page "Page1"
6. Associate it to variant "A"
   1. on Page1, select "A" in the variant selector
   2. click the "Versions" button
   3. select "Link page to variant A"
7. Create a sub-page "Page1-1"
8. Associate it to variant "A"
9. Go back to Page1
10. Click the vertical 3 dots button, select "Administer Parent"
11. Go in "Look & Feel" > "Pinned Pages"
12. Select "Page1-1" and save
13. Create a publication setting ("Versions" button > "Publication" > "New")
    1. select version "v1"
    2. select variant "B"
    3. check "Publish page order"
14. Publish

Result

The top page of the book and Page1's administration page are published, appearing like this in the extension's navigation panel:

Note that Page1 was not published (as intended), but is displayed because a sub-page, Page Administration, has been.

Expected result

Only the top page of the book is published, appearing like this in the extension's navigation panel:

Remark

This is a minor issue. Guests can't see hidden pages and users can't see them either by default, so most users will see the expected result.