Inserting to content://sms/sent creates new conversation

When my app sends an sms, I use .insert into content://sms/sent. That works, but for some reason, in the conversation list, (default Desire messaging 开发者_JAVA技巧app) a new conversation appears in addition to the already existing one with same phone number. It happens no matter which contact I choose. When inserting, I only use the phone number and message text. I guess I need to specify person somehow. The question is how? I get the contact using contact picker.