Moo Menu - child objects not staying when i browse articles

Hi there, can someone please point me in the right direction,

When i select a main item on my menu, the child objects show in a row below, which is exactly what i wanted, however if i then click on any item or link on the page the child menu disappears and you have to click the main menu item to see the child objects again ?

Is there any known issue with this ?

Thanks in advance.