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.