When the base class contains non-throwing virtual functions e.g.

class Base {
    virtual void f() noexcept;
    virtual void g();
};
class Derived : public Base {
};

Then using Insert Virtual Functions refactoring action results to

class Derived : public Base {
    void f();
    void g();
}

As each overrider of non-throwing virtual function must be non-throwing, the derived functions must specify noexcept. Thus the current result is ill-formed.