When entering conditional Smarty Code in e-mails or pdf letters in the source code view, switching to WYSIWYG-view and then back to source code, special characters are transformed to their HTML code equivalents, e.g. double quotes become """, inverted commas become "#39;". This leaves the smarty syntax broken, of course, and forces the user to undo the changes made to the special chars anytime (s)he switches back to source code view.
This is a source of error in the mail or letter workflow, and if there's a chance of keeping the chars from being transformed when switching (back) to source code, this would be a great improvement.
I've tested this issue on the official demo.