Possible Optimization bug

For the following code:

#include <iostream>
#include <vector>
int main(int argc, char *argv[])
{
    int const dimension = 2;
    int const number_of_nodes = 20;
    std::vector<double> x(number_of_nodes*dimension);
    for (int n=0; n<number_of_nodes; ++n)
    {
        x[0+dimension*n] = 0.01*n;
        x[1+dimension*n] = 0.02*n;
    }
    for (int i=0; i<40; ++i)
        std::cout << "x["<< i << "]: "<< x[i] << std::endl;
    return 0;
}

I get the wrong output with -O3:

x[0]: 0
x[1]: 0
x[2]: 0.01
x[3]: 0.02
x[4]: 0
x[5]: 0
x[6]: 0.03
x[7]: 0.06
x[8]: 0
x[9]: 0

...

I get the correct output with -O2:

x[0]: 0
x[1]: 0
x[2]: 0.01
x[3]: 0.02
x[4]: 0.02
x[5]: 0.04
x[6]: 0.03
x[7]: 0.06
x[8]: 0.04
x[9]: 0.08
…

I get the same results with versions 15.0.090 and 15.0.3. This does not occur with 14.0.4.

Any help would be appreciated.

Thanks.