I can't move back into the text in books/signs, if I made a mistake, I must delete everything after it!

I can't move back into the text in books/signs, if I make a mistake, I must delete everything after it!
What I expected was to move back and forth freely through text in signs and books!
What actually happened was that I could not go back through the text, if I realized a mistake, I had to delete everything after it!
I could not find this in the Navigator, I tried "Sign" and "Type" and "Sign Type Arrow" and "Sign Type".
Anyway, to catch out the bug:
1. Open a sign
2. Type anything
3. Try to move back, it won't let you, not without deleting everything after!