Not sure if this has been reported already, but I am having this issue where when I hit send, I get the Leave/Cancel dialogue box. Of course if I hit Leave, my message or post doesn't get sent. So I hit Cancel and then hit send again and it works.
I also had, and still have this problem, which I got over with trial and error.
After writing my message, I press the send button, and I also get the cancel/leave button appear.
Firstly, I used to press cancel, which wold return me to my original message, then I would press send again, and the message would be sent.
Now, I just press leave, and the message has gone. This is confirmed by checking my'sent box'.