The Microsoft Office blog is reporting a known problem with CSS definitions. The specific areas affected are number and bulleted lists.
They note that this problem has been resolved in newer builds. The workaround specified for the beta is to simply restart Outlook.
The full description and resolutions can be found on their blog.
http://blogs.msdn.com/outlook/archive/2010/01/22/issue-with-message-sizes-in-outlook-2010-beta.aspx
