background disappears on "some" pages issue

hi
i'm using maximenuCK for a website www.deco-nuances.com

however, on some pages like this one: www.deco-nuances.com/index.php/contactez...t-desormais-possible the background of the submenus disappears and becomes unreadable...
is this a known issue?

thanks

PS i temporarily solved it by deactivating mootools effects... which means it comes from this... hopefully it will be solved, otherwise if you need the issue to be "activated", i'll use mooeffect again next tuesday (the day i work for this client), so we can check together... in the mean time i can't allow myself to put the issue online or the client will not be happy...

noone?
i'll put the site back with mootools today, and disable it tonight, so you can have a look at what i mean and eventually help...
it most of the time happens with menus when on a page in the slideshow