PHPBB3 has a bug with IE8 or the other way around.
This is giving you problems when you want to edit larger posting on the forum.
The cursor keeps jumping up with every letter you type, so very annoying
Solution for now is to add the forum URL to the IE7 Compatibility list in IE8
Go to menu option Page and add the URL with Compatibility Settings.
From then on the forum will start in IE7 mode and editing works fine
I'm waiting for the definite fix on this.....