Make sure the event is 'Unit starts effect of an ability', if u use 'Unit begins casting an ability' it maybe doesn't get the target point, i guess.
Also, make sure your spell targeting a point not an unit.
In short, if the game cannot determine the destination point, it will return center of the map as default.
If u order unit y to move instantly to the position of unit x, but a unit x is already die, then unit y moved to center of the map.