Another strange thing is that despite I wasn't resetting the matrix the objects in the scene didn't move at speed of light   as I would expected. I mean in OpenGL if you don't initialise the transformation matrix at each loop it is used (multiplied) as it was left in the previous loop, so for example if you have a matrix with a translation of 2 point on the X you continue to translate of 2 point each loop (at 60FPS you should your objects run away at 120 points/second!).