  We present three different theoretically foreseen, but unusual, astrophysical
situations where the gravitational lens equation ends up being the same, thus
producing a degeneracy problem. These situations are (a) the case of
gravitational lensing by exotic stresses (matter violating the weak energy
condition and thus having a negative mass, particular cases of wormholes
solutions can be used as an example), (b) scalar field gravitational lensing
  (i.e. when considering the appearance of a scalar charge in the lensing
scenario), and (c) gravitational lensing in closed universes (with
antipodes).The reasons that lead to this degeneracy in the lens equations, the
possibility of actually encountering it in the real universe, and eventually
the ways to break it, are discussed.
