Sorry but this is not a bug in mojoPortal.
This is a problem in your custom design and the designer should be able to solve it.
We have a forum for Help with Design and Skins, and other designers may be able to help you there with some questions.
When I viewed your site in Firefox I did not see any menu items fly off the screen. Maybe you are using IE or some other browser.
Main problem I notice on many pages of your site is you are using huge image files and this is killing your site performance for users. You should fix it by optimizing those images before you go live with this site.
Anyone visiting those pages for the first time will see those pictures scrolling into place because they load so slow because they are way too large for web site images. All the images on this page for example are too large http://mojoportal.kshousingcorp.org:85/governance.aspx
It may seem fast once the images are cached by your browser but those images really need to be fixed.
Hope that helps,
Joe