Unwanted horizontal scrollbar in IE6

Here's how the issue can be reproduced:

• XE 1.9 SNAPSHOT 17115 + IE6 on WinXP
• Edit a page with the new WYSIWYG editor
• Enter content into the page and hit enter
• Repeat the process until you reach the end of the content area
• A vertical scrollbar and a horizontal scrollbar appear

The horizontal scrollbar shouldn't appear (it doesn't appear on FF3)