What's your browser ?
If the focus in on a text box, it isn't supposed to go back to the previous page.
At worst, add a keyboard object and add a blank "On 'backspace' key pressed" event.
It should catch the key and cancel the normal usage of the key.
Also, be sure to use the "Edit post" in "Post options".
Bumping the thread after 24 hours is OK, but if you want to add more informations to a previous post, editing it is a better fit.