sub menu are not showing correctly

Hello,

I have a problem in Storebox template.
In mega menu, I Have third level group. When I try to mouse over on it, sub-items keep in the wide of my second level (so I can't see all sub-items).
You can see the problem here : "Produits" / "certificat de conformité européen" : there should be three items, but the sub menu sdoes'tn expand...
http://www.gedautomobile.com/

Thank you in advance for your help.

Hi

Is it related with some specific browser? I can see it fine in FF, Safari, Chrome: