Why does uniform initialization in C++11 behave weirdly with virtual base classes?

Right now, I am learning the features of Inheritance in C++ and wanted to test out the recently learnt concept of Virtual Base classes. I tried the following simple code:

#include <iostream>

using namespace std;

class A
{
private:
    int m_value;
    string m_caller;
public:
    A(int p_value, string p_caller) : m_value{p_value}, m_caller{p_caller}
    {
        cout<<"Instantiating A via "<<m_caller<<endl;
    }
};

class B : virtual public A
{
private:
    int m_value;
public:
    B(int p_value1,int p_value2) : A{p_value1,"B"}, m_value{p_value2}
    {
        cout<<"Instantiating B."<<endl;
    }
};

class C : public B
{
public:
    C(int p_value1,int p_value2) : A{p_value1,"C"}, B(p_value1, p_value2)
    {
        cout<<"Instantiating C."<<endl;
    }
};

int main()
{
    C c1(1,2);
    return 0;
}

Please note the B(p_value1, p_value2) in the constructor of class C. This gave me the desired output:

Instantiating A via C
Instantiating B.
Instantiating C.

But, the moment I changed it to B{p_value1, p_value2}, I got the following output:

Instantiating A via C
Instantiating A via B
Instantiating B.
Instantiating C.

I tried looking for the answer, but all the answers I got quoted some C++ standards. Being a beginner in OOPs, I am looking for a simpler explanation for this behaviour. Thanks a lot!

P.S. I am using C::B in Windows with compiler g++ 4.8.1.