C++ random values and Blitz++

The code below is compiling and running. The code should init a Blitz-matrix to random values but it fails as every element of the matrix got the same value.

#include <iostream>
#include <array>
#include <algorithm>
#include <functional>
#include <random>
#include <blitz/array.h>

int main()
{
    // random
    std::random_device __device;
    std::array<int, std::mt19937::state_size> __seeds;
    std::normal_distribution<double> __distribution(0.0, 1.0);
    std::mt19937 __engine;
    std::generate_n(__seeds.data(), __seeds.size(), std::ref(__device));
    std::seed_seq __sequence(std::begin(__seeds), std::end(__seeds));
    __engine.seed(__sequence);

    // matrix
    blitz::Array<float,2> a(4,5);
    a=__distribution(__engine);

    // io
    std::cout << a << std::endl;
}

The output is not what I wanted

(0,3) x (0,4)
[ -1.10231 -1.10231 -1.10231 -1.10231 -1.10231 
  -1.10231 -1.10231 -1.10231 -1.10231 -1.10231 
  -1.10231 -1.10231 -1.10231 -1.10231 -1.10231 
  -1.10231 -1.10231 -1.10231 -1.10231 -1.10231 ]

What's the proper way to init a Blitz-Matrix to random values?