Hi Arjan, Thanks for the bug report - I found that it happens in both IE6 and IE7. This was such a bizarre thing - I still have no idea why or even how it possibly could occur, but I seem to have found an ugly but effective fix for it which I have added to the latest version of Superfish (now updated to version 1.3.2) which you can find in the usual place here: http://users.tpg.com.au/j_birch/plugins/superfish/
Cheers Joel Birch.