How do i make a deleted character disappear?

When I delete a character, it doesn’t disappear. It just turns brown and acquires a dash through it. If I delete it again, it doesn’t change.
Also, a vertical line appears in the left margin.
What is going on, and how can I fix it?
Thanks.

I found the answer. I turned off the Record Changes toggle (at Edit>Track Changes) and it’s tame again.