My girlfriend and I both have the same phone, HTC desire. We've both encountered this. If typing a reply to an existing text message, sometimes the text messages suddenly appear under another contact than the contact you sent them to. If I go to message details, I see that the message is indeed sent to the correct number, but is threaded beneath the wrong contact. It has been making me send another message to the wrong contact, apologizing for the wrongly sent message, leaving the recipient confuzed, as the message were never sent to her/him. I wonder if HTC is aware of this problem, and what can be the cause of this problem. We both have the facebook sync enabled, but I personally think this is some kind of bug that happens right after sending a message, somehow storing the message at the wrong contact thread.