Help to find crash in simple stack type?

[Gary Willoughby via Digitalmars-d-learn]

I've created a simple stack type using calloc/free which seems to 
work nicely. Then instead of using C functions i've tried to 
implement the same type using the GC. However i'm experiencing a 
crash. I've been staring at this snippet for hours now any help 
would be appreciated. This is a simplified snippet showing the 
crash:

import std.stdio;
import core.memory;
class Stack(T)
{
        private T* _data;
        private T* _pointer;
        private immutable size_t _minimumSize;
        private size_t _size;
        private size_t _count;

        public this()
        {
                this._minimumSize = 32_000;
                this._size = this._minimumSize;
                this._data = cast(T*)GC.calloc(this._size, GC.BlkAttr.NO_MOVE);
                this._pointer = this._data;
                this._pointer--;
        }

        public void push(T value)
        {
                this._pointer++;

                if ((this._size / T.sizeof) < (this._count + 1))
                {
                        this._size *= 2;
                        writefln("realloc to %s bytes", this._size);
			this._data = cast(T*)GC.realloc(this._data, this._size, 
GC.BlkAttr.NO_MOVE);
                        this._pointer = (this._data + this._count);
                }

                this._count++;
                *this._pointer = value;
        }
}

unittest
{
        auto stack = new Stack!(int);

        for (int x = 1; x <= 300_000 ; x++)
        {
                stack.push(x);
        }
}

It seems to crash when the loop iteration is at about 260,000 and 
i've no idea why. I'm using Ubuntu 64bit latest DMD.