Audio Systems: Pioneer VSX-D902S does not put sound through only te headphones.

Question
I have a Pioneer VSX-D902S that, even though headphones are plugged in, the sound comes out of both the headphones and the speakers. I would like it to only come out of the headphones in this case.

Answer
I am having a little trouble finding and documentation on this unit. May you please look at the back of unit and give me the a part number from there. Sometimes the model number on the back is different then whats on the front, I really wish I knew why manufactures did that it makes no sense. It should be a tag with the Serial number model number and possibly a version number i just need the model number.