Oh, found another answer that seems to have answered this. The first parameter needs to be null, not that last parameter as indicated in the above link.
onmousedown='return DayPilotCalendar.dragStart(this, 60*30, "125", this.innerHTML);'
should be...
onmousedown='return DayPilotCalendar.dragStart(null, 60*30, "125", this.innerHTML);'