CONFIRMED - Same thing happens on www.mediawiki.org as it did on en.wikisource.org
Open any page to edit mode and try to insert any character from the CharInsert bar to the textarea.
The character selected is not inserted and it seems the "focus" goes to the top of the page instead. Here's what IE's F12 reports upon insertion attempt.
function anonymous(evt) { mw.toolbar.insertTags('₡', '', ''); evt.preventDefault(); return false; }
SCRIPT5007: Unable to get property 'insertTags' of undefined or null reference
File: Function code (722), Line: 2, Column: 1
SCRIPT5009: 'insertTags' is undefined
File: index.php, Line: 138, Column: 13