It happens occasionally. Not every text message gets duplicated, however it does happen at least once a day. I just checked some old text messages and it occurs with more than just one contact. It happens all the time when im texting my GF (she has a galaxy s3 on verizon) and i also noticed it with a friend from school (iphone 5, not sure of the carrier) as well as with my sister ( iphone on verizon).
I have a lumia 822 on verizon. this has been going on for some time now, i just recently thought to look on these forums for a solution.