Is this a bug or my setup

[#1]

When editing a post in IE8 where the length is such that the side bar is showing the post keeps bouncing about when I start typing part way down and it makes it almost impossible to see what I am doing.
It doesn't do it in Firefox. Operating system Windows 7 64 bit

[#2]

looks like it is a Wordpress bug http://wordpress.org/support/topic/290852
http://www.simplemachines.org/community/index.php?P=7fce62ac356fee632929741121c72795&topic=300154.ms...
Switching to compatibility mode fixed it

[#3]

A wordpress bug wouldn't affect the forums... sounds more like it's an issue in IE8 if it's affecting the forums too.