this issue is similar to
MDL-59920, so the description will be quite short at this point.
A user created an repeating event in the Moodle calendar. When he drags one event to another day, only this event is dropped.
As this event is part of a repeating event, when dragging and dropping it, a modal dialogue should open and ask if only this single event or all events should be moved to this new location in the calendar.
If any further information should be needed, please comment.