The letter now works correctly, thanks.
If it doesn't work for someone, you have to refresh your JS file. Refreshing the admin page for post editing doesn't work for chrome. What you have to do is when you're on the post (or page) edition page, right-click anywhere and choose "View source". Then ctrl+f (find) the following text:
wp-tinymce.php
It will be a link. Open the whole link in a new tab in your browser and hit CTRL+R (hard refresh). Then refresh the page with your post editing. It should work.
Thanks for fixing this.