Help to find crash in simple stack type?

[anonymous via Digitalmars-d-learn]

No explanation or solution, but a reduction:

import core.memory;
void main()
{
      alias T = ubyte;

      enum size1 = 2_049; /* > 2_048 = 2^^11 */
      enum size2 = 1_048_577; /* > 1_048_576 = 2^^20 */

      T* _data;
      _data = cast(T*)GC.calloc(size1, GC.BlkAttr.NO_MOVE);
      _data = cast(T*)GC.realloc(_data, size2, GC.BlkAttr.NO_MOVE);

      T* _pointer = _data;
      foreach(i; 0 .. size2)
      {
          *_pointer = 0; /* segfault at i = 1_048_576 */
          _pointer++;
      }
}