Draw Rectangle

I am trying to draw a rectangle, and it works when dragging my mouse from top to bottom, but not bottom to top and I have absolutely no idea why.

     GL.PushMatrix();
     selectBoxMat.SetPass(0);
     GL.LoadPixelMatrix();
     //GL.Color(Color.red);
     
     GL.Begin(GL.QUADS);
     GL.Vertex3(mouseDown.x, mouseDown.y, 0);
     GL.Vertex3(mouseDown.x + 2, mouseDown.y , 0);
     GL.Vertex3(mouseDown.x + 2, mouseCurrent.y , 0);
     GL.Vertex3(mouseDown.x, mouseCurrent.y , 0);
     GL.End();

Ideas?