sequence of inheritance from virtual base class?

I have a problem with the sequence of inheritance:

    // header1.h
    class Base {
     public:
       Base() {}
       virtual ~Base() {}
       virtual void foo() = 0;
    };

    // header2.h
    #include "header1.h"
    class Unrelated1 {};
    class Unrelated2 {};

    class Derived1 : public Base, public Unrelated1, public Unrelated2 {
    public:
       Derived1() {}
       ~Derived1() {}
       void foo() {}
    };

    class Derived2 : public Unrelated1, public Unrelated2, public Base {
    public:
       Derived2() {}
       ~Derived2() {}
       void foo() {}
    };

    // main.cc
    // g++ -o main main.cc
    #include "header2.h"
    int main() {
       Derived1 d1;
       Derived2 d2;
       d1.foo(); // ok
       d2.foo(); // crashes in big app
    }

The problem seems to be the sequence of inheritance: if I inherit from
'Base' first (Derived1), the code seems to run ok. If I inherit from
'Base' last (Derived2), the code crashes reliably at runtime in a
seemingly unrelated code position (other class, other function, but
always the same).

The crash happens when Derived2 comes from one shared lib, Derived1 from
another. Calling a non-virtual function in Base seems ok, the crash
happens only when calling a virtual function in Base, so it looks to me
like a wrong lookup in the virtual function table.

This happens on Windows with Microsoft cl and on Linux with g++.

I've checked the FAQ for multiple inheritance issues but found nothing
related to this. It also does not matter whether I use
   Derived2 : ... public Base ...
or
   Derived2 : ... virtual public Base ...

Shouldn't this code be independent on the sequence of inheritance?

Thanks for any insights...
R'

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