Working demo on JSFiddle - https://jsfiddle.net/y5ykm415/4/
So, quick summary of events order:
Draggable element on mouse click (mousedown) executes drag start event and actual dragging begins
All droppable elements activate an wait for droppables.
Draggable's drag event executes again and again on each, smallest mouse movement.
When draggable reaches droppable and meets tolerance and accept conditions, it(draggable) can be dropped on ...