It's really annoying when your sent text says it's a draft, isn't it? This happens to me all the time, and I get confused!
From your messages, it will look like the message that you definitely know has been received by the recipient, has in fact just been saved as a draft. By why does your phone do this?
It happens after you've sent the text, and before going back to the screen showing all the messages, and can be caused by accidental taps after you send the message, or hitting the send button too many times. Tapping other keys while the message is being sent can also do this...
It's most likely that you pressed the space key a couple of times, making the text look blank so just showing the message you sent previously.
So, what do you do to resolve this?
Simply open the text message that states it's a draft, and press backspace until you can't do it any more. Go back to the main messages screen and you should see that the draft message has disappeared!
Hopefully this solved the problem. It really is annoying - but luckily there is a simple explanation!