Why is this object a Proxy only when the page field is 1?

Steps to reproduce:

1. Open the reproduction

2. Open the browser console

3. When the project starts it will errors with:

   Uncaught (in promise) DOMException: Failed to execute 'put' on 'IDBObjectStore': #<Object> could not be cloned.

   This is happening because IndexedDB cannot serialize and persist a Proxy object which is pagination in this case.

   But...

4. If you click on "Next" button the pagination changes from {"page":1,"size":5} to {"page":2,"size":5} and IndexedDB persists the object with no issues!

5. Even stranger: if you click on the "Previous" button it changes from page:2 to page:1 and the error is here again!

Why the first page is a Proxy object and the following pages not?