IE7 display bug of menu-"children"

Hi ppl,

ok, this is my the first Issue here.

at first of all: my testweb: http://nova.billa.sk/ (web is not finished yet)

there is in the bottom of header section, the main navigation consisted of 8 menu items. each of these menu items is individual Nice Menu, which has its children and some of them have also sub-children.

The problem is clear. This complex of menus is compatible in firefox 3, opera, safari, google chrome, IE6 and partially in IE7

Why partially? Because once it works, once not ....it's strange.

Let me explain u whats going on:

when I move mouse over the main menu item / 1st submenu list , there is also automatically shown the 2nd submenu (but empty) list, ........ then, when i move mouse on the submenu item where this 2nd submenu list belongs, then the content of the 2nd submenu is shown.

problem is, the 2nd submenu (empty) is being shown earlier than I move my mouse over his parent. This problem is ONLY in IE7. And also there is something wrong, because

if it's OK, then it's OK
if its wrong, then it's wrong
.....but this is sometimes OK and sometimes wrong ....

Who can help me? I think it is question of CSS output, but in my opinion its some trick in CSS for IE7 or something.
Maybe I am wrong and I did a mistake, when i was modifying css for these menus. But I can't where is this problem hidden >.<.

here is css of this menu (on first sight it seems, that its written a bit messy, but experienced css coder will find a way how to find out the problem):
http://nova.billa.sk/themes/billa/menu.css

Thank you.

Here are screenshots related with this problem