Backspace not working on signs, chat, book & quill

I was in a world on Xbox one (recently updates to 1.2.9) and when I send to chat I made a mistake. I went to do a backspace and it wouldn't work. I tried it on a keyboard and it didn't work.

Steps to reproduce:

1. Place a sign.
2. Type words rapidly enough to invoke the lag described in MCPE-28255.
3. While the lagging text is being displayed, press the Backspace key.
4. Observe that pressing the Backspace key no longer has any effect.
   The problem doesn't happen every time, so you might have to repeat this procedure a few times.
   Also see comments below about persistence within and across worlds.