请看我的代码。我有一个基类“System”和一个派生类“AdvancedSystem”。当访问基类引用时，输出是未定义的和随机的，我不知道为什么。如果派生类给了我预期的输出。有什么想法吗？

#include <iostream>
#include <vector>

class System {
public:
    System() :
        someValue(12345)
    {}
 
    int someValue;
};

class AdvancedSystem : public System {
public:
    AdvancedSystem()
    {}
};

class Strategies {
public:
    Strategies(System& system) :
        system(system)
    {}

    System& system;
};

class Test {
public:
    Test() :
        system(),
        strategies(system)
    {}

    AdvancedSystem system;
    Strategies strategies;
};

class Tests {
public:
    void createTests() {
        for (int i = 0; i < 18; ++i) {
            values.emplace_back();
        }
    }

    std::vector<Test> values;
};

int main() {
    Tests tests;
    tests.createTests();
    std::cout << tests.values[0].system.someValue << "\n"; // outputs expected value of 12345
    std::cout << tests.values[0].strategies.system.someValue << "\n"; // outputs random number
}

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