Vista - Menu control/css problem

I've tried this question on the menu controls forum but got no answers so
I'll try again here.

I have a website that is based on the small business starter kit
(http://www.asp.net/downloads/starter...mall-business/). I am having
problems getting 2nd level dropdown menu options to work properly. Basically
the div which contains the menu has rounded edged images at either side and
this is interfering with the background of the dropdown options. I have tried
and tried to get it to work and am now seeking help as I must be missing
something.

It's easy to reproduce the problem on the starter kit as the web.sitemap
already has a 2nd level menu option under Items. So all I did was set the
Menu MaximumDynamicDisplayLevels to 2 in the master page and the problem
appears.

Thanks for any help or advise you can give.