I am not sure what is causing this but I noticed it after I upgraded from OS 5 to OS 6. What happens is I type someone's name and in the search there contact comes up, I then hit the BB key, go to text them, and it asks which number. For example, one contact has a mobile, work, and 2 e-mail addresses that are the same! I am not sure why this happens and it's with more than one contact. Was it something when I upgraded that it just added the duplicate? I'm not sure but if it can't be fixed I guess I will have to wait until I get a new phone.
Try going into contacts then - options - general options - allow duplicate contacts = no
Not sure if that is your problem or might be having two backups of contacts. I had the same issue and had my contacts back-up on outlook through DM and gmail wireless. I've since turned off the DM backup through outlook and stuck with gmail wireless only and so far no issues.
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