Is the shingle at the low side of the vent part of the shingle course, or is it just a cut piece of shingle that was applied over the metal base flashing of the vent? I can't quite tell from the photo. If it's part of the shingle course, it's wrong and a leaker. If it's applied over the base flashing strictly for cosmetics, I would say it's okay but kinda stupid. Even if its fully bonded to the metal base flashing and water could get trapped between the applied shingle and the base flashing, I can't see how water could get into the house.