Problem with glDrawElements when using a buffer offset

Hi,
I can draw my scene no problem if I use:

gl.glDrawElements(GL.GL_TRIANGLE_STRIP,num,GL.GL_UNSIGNED_INT,0);

Which would draw elements 0…num from the element array buffer.
However, I’d like to draw specific parts of the element array, eg:

gl.glDrawElements(GL.GL_TRIANGLE_STRIP,num-2,GL.GL_UNSIGNED_INT,2);

Which would draw elements 2…num.
My problem is that this doesn’t work, and not only that it will often manage to completely crash the entire machine.
I understood the last parameter “indices_buffer_offset” in glDrawElements() to be the offset into the element buffer from which to start rendering, with “count” elements being rendered.

Am I making a mistake, or is this a bug?

Thanks,
Chris.