Backspace out of a page deletes reply

I have had this problem a couple of times today, and on two separate computers. I have been typing a reply to someone, and do a few clicks inside the text box while editing, and then hit the delete/backspace button (I'm on a Mac) and it takes me to the last page rather than deleting the text I was editing. When I hit forward, my whole reply is gone.

As you can imagine, this is rather infuriating, especially when time is short, or it was a lengthy reply. Could you either implement a method of saving the text in the text box when "back" is pushed, or ensure that the cursor remains inside the text box?