onMouseEnter not called while dragging

I'm trying to implement a drag&drop feature in my game's GUI, where the user can drag an image to an empty space in the gui. I've added a BeginDrag and EndDrag events to the dragged UI item, and a "MouseEnter" event trigger to the empty spaces in the UI (so I can tell where the user wants to make the "drop").

The problem is that the MouseEnter event (in the target GUI) is only called AFTER the release of the drag (in the dragged GUI), even if the dragged item (which is attached to the pointer) enters the empty space, or when the user isn't dragging anything.

So, my question is: Is it by design in Unity to not call "mouseEnter" event while a drag event is being performed? If so, how can I workaround this?

Thanks.