OpenMP map(alloc) not working for arrays (SIGSEGV)

I'm trying to use local arrays in an OMP target region. If its size is dependent on a variable, the device will crash with a SIGSEGV "offload error: process on the device 0 was terminated by signal 11 (SIGSEGV)"

Code: 

#include <stdio.h>
#include <stdlib.h>

int main (int argc, char *argv[]) {
  {
    int size=argc*100000;
    int ar[size];
    int ar2[100000];
    printf("Size host %lld %lld\n",sizeof(ar),sizeof(ar2));
    #pragma omp target map(alloc:ar,ar2)
      printf("Size device %lld %lld\n",sizeof(ar),sizeof(ar2));
    printf("Size worked\n");

    #pragma omp target map(alloc:ar2)
      ar2[size-1]=55;
    printf("Static worked\n");

    #pragma omp target map(alloc:ar)
      ar[size-1]=55;
    printf("Dynamic worked\n");
  }

  return EXIT_SUCCESS;
}

If you run this you get the output:

Size host 400000 400000
Size worked
Static worked
offload error: process on the device 0 was terminated by signal 11 (SIGSEGV)

Strangely: You can access lower entries (e.g. ar[0], ar[1]...) without problems (not sure if they are valid though) and using "10000" as the size does work (at least without a crash). Also doubling the size of ar2 works. Is this a compiler bug or do I have to use this as an array section? If so, can you point me to the OMP spec where this is explained?