The SdrPage copy constructor contains the line
    *this = rSrcPage;
Like in issue 93186 this leads to slicing and to subtle errors.

The copy constructor SdrObjList also contains an assignment to *this.

Avoid assignment to *this.

One way to do this is the use of a proper Clone() method.
For details on the general problem see for instance item 54. Avoid slicing... in
C++ Coding Standards by Sutter and Alexandrescu.