Well.. i feel that there is something wrong with this exception. Firstly, for an artist to draw a portrait, the artist is paid to do so. And in normal circumstances, the drawing/portrait is owned by the person who commissioned the painting. Reproducing an exact portrait is really difficult and requires hard work / talent and skills with his brush. For a photographer however, reproducing an exact copy of the image is just a simple copy. Not much hard work involved here. That leaves the person who commissioned/engage the services of the photographer at a disadvantage as he paid for the service and yet loses his copyright for his image. I guess something should be fixed here. So long that the photographer is being paid by an amount that the photographer is willing to accept for the job assignment, the copyright should remains with the person who paid for it. Permission should be asked instead by the photographer if he wishes it to be used for his portfolio.
Take an analogy, an advertisment designer, who designed an ad could not claim copyright for his advertisment design. The advertisment is own solely by ad company and not him. He can't use it if he decides to work for another company. However, if he decides to work for another company, and wishes to use his previous design, the new company can negotiate for the use of his work with his previous company.
Thats why.. i can't figure out why there are these 2 exceptions. There should not be any exceptions at all. So long the the photographer is being paid for what he had asked for, he shouldn't claim any copyright at all.