I don't know...
I have a problem where sending phone numbers to"dumb phones" appears blank.and if it's part of a message, the rest of the text show up, but not the number.
I've had to resolve to spelling out the digits so the contact info can be read!
I wonder if Go SMS is over zealously detecting some forms of data and sending out non standard text as a result.
Have you tried to see if the stock browser sends duplicates as well?