Maybe our perception of photons is influenced by its phase. The second polarizer shifted all photons beyond 180o phase and we don't perceive them.
A third polarizer pushes some photons back beyond 0o phase and once again become perceivable; hence a brighter region.
This would suggest that by pushing photons reflected off any body to the negative phase (>180o), it is possible to 'phase' it out of view. Invisibility!