How to drop item from screen?

-InventorySlot-
Dragging Item and moving it with other slot seem do execute and printString, but dragging away from inventory/Dropping from screen do not execute the OnDropFunction and even printString.

It executes when the DraggedItem is dropping inside/area of the inventoryWidget.

-Inventory- (itself)
Even InventoryWidget only executes when inside/area of the InventoryWidget.