Im guessing you have no construct/destruct hooks.
In this case you need to tell the listview to use
the built in ones:
MUIA_List_ConstructHook,
MUIV_List_ConstructHook_String,
MUIA_List_DestructHook,
MUIV_List_DestructHook_String
The built in one makes internal copies
of the strings so they dont dissapear.