When using the built-in AJAX Spell Checker of the Editor, on the first misspelled word the corresponding popup opens. When the user finishes with the first word, the same popup should open for the following word, but under IE11 this does not happen and the user is forced to click on the word for the dialog to open. To resolve this you can force the IE11 browser to IE10 compatibility mode with a meta tag in the head element pf the page <meta http-equiv="X-UA-Compatible" content="IE=10" />
The issue is fixed as of Q1 2015.
For me, in IE11 the misspelled word popup does not even open on the first instance of the misspelled word. I have to click on the misspelled word twice before it opens. It works fine in IE10.