I'm on Verizon using a MotoX 2nd generation, and my phone started doing the same thing. After typing the text message it will display "sending", then clone and send the message multiple times, each time with an icon that looks like a text message with a check mark on it. I can stop the process if I delete the original message. It seems to do it primarily when I'm sending messages to iPhones. Interestingly, the same icon appears when my phone is in the car and sends an auto-reply to a received text message, but doesn't appear if the text messaging sends normally. I've had the phone for over a year, but it only started doing this within the last 2 months or so. Running Android version 5.1