Wrong cursor behavior after changing format and pressing right/left arrow key.

Steps for Reproduction

1. Visit https://quilljs.com/playground/
2. Write some text
3. Put cursor in the middle of text
4. Change format, e.g. turn bold on
5. Press right arrow key - cursor jumps to the end of text
   or
6. Press left arrow key - nothing happens (second pressing works)

Expected behavior:
After pressing right arrow key, cursor should move one character right.
After pressing left arrow key, cursor should move one character left.

Actual behavior:
After pressing right arrow key cursor jumps to the end of text.
After first pressing left arrow key nothing happens.

Platforms:

Win10,
Firefox 52.0.2 (64 bity)
Chrome 57.0.2987.133 (64-bit)