Strange Behaviour

Eigen::Vector3f t = (-1,0,0);
Eigen::Vector3f tdx = (-0.999,0,0);
#pragma omp parallel for shared(t,tdx) private (i,j)
    for i = 1:m
        for j = 1:n
            if (omp_get_thread_number() == 0){
                std::cout<<t<<std::endl;
                std::cout<<tdx<<std::endl;
            }
        }
    }
Result:
(-1,0,0)
(-0.999,0,0)


Eigen::Vector3f t = (-1,0,0);
Eigen::Vector3f tdx = (-0.999,0,0);
#pragma omp parallel for private (i,j,t,tdx)
    for i = 1:m
        for j = 1:n
            if (omp_get_thread_number() == 0){
                std::cout<<t<<std::endl;
                std::cout<<tdx<<std::endl;
            }
        }
    }

Result:
(0,0,1e-32)
(1e+34,0,1+e23)

Why is it undefined when I use t,tdx as private?