You should make it possible to cancel event dragging by pressing ESC.
For example: I click on event and try to relocate it (change date/time). But if I want to cancel this move and I forgot the start date/time - I have no chance to cancel it - I can leave it somewhere, but then the date or time will be wrong.
It happens very frequently…
You can just add a key listener and if user click on ESC while moving an event - the event will be placed back to the original location and NOT updated.
I added a picture for better explanation.
