The sanitize_callback is called twice when the option is saved the first time in the database

[inf3rno]

I have an array option containing many booleans coming from checkboxes.
Initially the database options table does not contain this option and the booleans are coming from its defaults array.
When I check a checkbox and save the option the first time on my admin page, then sanitize_callback is called with {"x":"on"} input the first time and the output is {"a":false,"b":false, ..., "x":true}. After that the sanitize_callback is called a second time with the input {"a":false,"b":false, ..., "x":true} and because isset(false) is true I got {"a":true,"b":true, ..., "x":true} as the output, which is saved to the database.
When I change a value again on my admin page the sanitize_callback is called only once with {"a":"on", "x":"on"}, which is the normal behavior.
I am sure this is a bug because the sanitize_callback is called with already sanitized data the second time.
Others found this too two years ago, but apparently nobody reported it. ​https://stackoverflow.com/questions/71974444/wordpress-register-setting-sanitize-callback-runs-twice-on-initial-save

[inf3rno]

Duplicate of #21989.