I am very concerned with your last response. Of course if you build (and I have) a static menu with multiple levels all is OK.
This only happens with a dynamic menu. In the dynamic case, the starting left position of a level is determined by the ending right position of the level above. In the static case, the starting left position of a lower level is determined by the starting left of the main level. There is a distinct difference.
Please refer to cssmenutest.php for proof of static menu.
Now look at the third level of the products menu on omabeta.shopoma.com.au Please note that I can't leave the menu structure like this forever.
I had the initial width of the three levels set to 150 px and all was OK. I then reduced the width of Level 2 to 130 px which results in a gap between level 2 and level 3. If I were to increase the width of level 2 then it would overlap level 3. The problem is that CSSMW is not recalculating the left position of the next menu down.
You need to do this yourself on your own dynamic menu to find out.