Wrong autocompleter top position when scrolling on Administration 'WYSIWYG Editor'

• Go to Administration -> WYSIWYG Editor
• If you leave the page as it is (no scrolling) the position of the 'Plugins', 'Menu Bar', 'Tool Bar' suggests are correct, see correctPosition.png
• If you scroll a bit the page, the top suggest positions get messed up, see wrongToolbar.png wrongMenu.png

The #suggestion inspect also displays

<div id="suggestions" style="position: absolute; left: 263px; top: 470px; width: 165px; display: none;" undefined="display:none">