Hi,
You should simply have an Fsm on each slot, and set it up to receive ngui events like on hover and then have the logic on each slot.
if I take the ngui example "Drag & Drop", it all works fine.
I select the gameObject "DragDropSurface", then I add a "NGuiEventsToPlaymakerFsmEvents" component, then an fsm, and I add to that fsm a "NGUI / ON DROP" Global event ( double check that in "NGuiEventsToPlaymakerFsmEvents", that event turns green.
and when you press play, drag and drop an itemm and the fsm will received that drop event. NOTE that to know what gameObject was droped, you need to use the action "get event info", the dropped GameObject reference is in "gameObject Data"
GOing this way, will definitly increase your flexibility and prevent having to mess with hardcoded bool variables and global variables.
Bye,
Jean