jQuery Vertical Mega Menu behaves unexpectedly

Hi,

I’ve an issue with that menu. I use about 7 top level menu entries and about 15 more located as submenus. Whenever I click on one of the menu entries to open a page, the page opens but the menu on the new page gets “repainted” in two steps: 1. the menu appears as a long list, containig 22 menu entries in one large row. Then it takes about half a second and the menu then is shown formatted correctly. Only the 7 top level entries are shown as expected. This behaviour is very annoying. I also tried the jQuery Vertical Accordion Menu but it bahaves the same way. Also in a quite fresh wp installation. Does anyone knows what might be wrong ? Or what vertical menu plugins can be recommended ?
All I need is a vertical menu that doesn’t “jump around” when repainted..

thanks for your help!
Thorsten